I think my record was around 17 pairs. Right now, it is 5 pairs.
I just might be a female-hating misogynist male chauvinist pig IRL (not saying I am, just that I might be), but I’ll be every female’s hero about this. When I get to be the CEO of a Fortune 500 company, our corporate policy shall be that no employee shall ever be required, encouraged, or pressured into wearing high heels or stilettos.
Maybe I’m totally missing something here, but I’ve never understood why high heels (especially stilettos, literally “mini-stilts”) have any appeal whatsoever to anyone, whether user or observer. Stilettos, in particular, have always looked to me like they must the direct descendant of the old Chinese foot-binding tradition.
Right now, there’s one shoe under my desk…the one on my right foot.
My left foot is broken and has a big clunky boot thing on it. I would not call it a shoe. 
Checking there, I see a surge protector, a piece of paper, and more dust than there should be. But no shoes.
Not literally under my desk, but in the office:
2 Pairs of sneakers for going to the gym - 1 for regular workout and 1 for running.
2 Pair of motorcycle boots (usually only 1 pair if I brought the bike that day, but yesterday I inadvertently wore the sneakers home so I had to wear my 2nd pair of boots)
I don’t keep extra shoes at work - what happens if I want to wear them out and I can’t get to them! No, all my shoes are in my closet where they belong.
What I do is choose the shoes I want to wear at work and I have a large laptop bag that I reserve one of the compartments for shoes. Then to get to work I either wear flipflops or rain boots or actual warm boots depending on the weather.
It’s not about not being able to wear my pretty shoes to commute in because they hurt, it’s because they’re freaking expensive and I’d rather not get them covered in snow/salt or wear the leather off the heels while driving.
I’ve definitely gone through periods where I stored shoes at work but I sacrificed a drawer of file space so they could be locked up. Weird crap disappears at offices. Laptops can be unsecured all day long, but leave a novel on the corner of your desk and poof!
Not under my desk, precisely, but I have a coat cabinet and they are stacked in there.
Let’s see, I’ve got 1 pair of heels in case grownups show up, 1 pair of steel toes if I have to go out to one of the sites, 1 pair of tennies for noon-time walking, and 1 pair of black flats for ouchy feet days.
That’s not too bad, is it?
I tend to remain barefoot unless I have to get up and leave the office. 
The IT guys I work with just say, “Please move the shoes out from under your desk.” Using one’s words to communicate requests can be highly effective.
I have a pair of steel toes and a pair of running shoes with osha toe covers. The steel toes hurt my feet so I got the osha toes so that I could wear them over my current shoes however they are not comfortable on my regular sneakers and had to put them on an old pair of sneakers with a lower profile. And since I have orthotics in my regular shoes I kept forgetting to change my shoes until it reached the point I never put on my saftey shoes. Hoever they are making noises about safty shoes again so I will probably have to dig them out here soon.
I also keep a spare shirt in my desk, actually two now since they gave me a polyester shirt as my “christmas present” and I stuck it in the desk drawer. This is in case of a catastophic spill of someones soft drink or somehting (which has happened).
I am NOT a female hating misogynist male. I like folks, ladies included. Hating folks just takes too much energy for me to do that.
When I was “the man in charge”, I told my “subordinates”, that they could wear almost any foot wear that they wanted to. I expressly mentioned that high heels were not required, nor encouraged.
On the shop floor, steel toed foot wear was required. Did you know that they actually make steel toed high heel shoes? I was blown away when one lady wore a pair to work. They were certified by the US government to be used where steel toed foot wear is required. Strange stuff! As long as she wanted to wear them & they met the specifications for our shop, I was OK with them.
BTW, I agree that high heels should be avoided at all costs. I also see no advantage to their use. I do see some possibility for health issues from their use. Why anyone would choose to wear them is beyond my comprehension. Oh well, to each their own.
Back to the OP’s question. Right at the moment, none, my feet are bare as we speak. When I am working away from home I wear one pair of shoes/boots for the entire day.
There may be a pair standing at the wall, but under the desk? Usually none, either at home or at the office. It’s one of the things I like best about that office
I have two shoes. One pair. Period. Under my desk or in my home or in my car or on the street, depending on where I am. The experience of the OP is completely alien to my life.
If a pair of heals that are worn once every week or so and have never been outside gets you so het up, you do NOT want to see the ladies room!
Do you work out? Wear a suit? What if it’s snowing/raining? What if it’s hot? You have one pair of shoes for all those scenarios?? No runners or boots or sandals? Besides the 14 pairs of shoes at work, I have at least that many again at home plus leather boots, winter boots, rain boots, hiking boots. I don’t think I even have a lot of footwear!
Female. Professional, office type workplaces for the most part over the last 30 years. Zero shoes under the desk. Never has been, never will be.
My shoes are a pair of black sneaker-type shoes that can pass as non-sneakers. I don’t wear suits if I can help it…weddings and funerals. These shoes pass. They’re sneakerish, so I can wear them to work out. If it’s raining or snowing…shrug…they’ll dry.
Now, understand, I have one prosthetic leg, so it’s easier for me to leave the shoe on the fake foot (it’s a bitch to get off and on) and just wear one pair of shoes than to change it whenever I want to change shoes. But the one pair thing precedes my amputation. I just don’t need multiples. I don’t do fashion.
I have various spare shoes at work, mostly in a file cabinet drawer rather than under my desk. One pair is maybe 2" heels (with a nice sensible cushy cork insole and a strap over my instep so that they stay on). I bought them for those rare occasions (weddings, etc.) when I might have to dress up, but haven’t managed to bring them home yet - they were ordered online and shipped to work. The rest are all flat and comfy - some are sandals that don’t require orthotics and the rest accommodate my custom orthotics. I wear comfy walking shoes to work, the type depending on the weather.
They are all quite comfy and pragmatic, except the heels (which are still comfy, as heels go). I haven’t actually worn the heels yet, except when they first arrived, I tried them on to make sure they fit.
Female in an office job for 25 years. Only the shoes on my feet. Once I wished I’d kept a spare pair in my car. It was the 80s. I was a substitute teacher in a pre k classroom. When the kids took their nap, I slipped of my shoes and read a book. A little girl came up and said she didn’t feel well. Then she gave evidence to the fact by depositing her lunch in my shoes. That was fun.
There are 2 pairs of shoes in my office right now and I’m not there. One is a particularly attractive pair of black heels that are unfortunately only comfortable for 4-5 hours at a time. They are one of my go to heels for days that I have high level meetings as they give me a little boost in confidence in my appearance, and I continue to hope they will hit that magic “broken in” yet still in good condition status. The other pair is non slip, OSHA approved and in case of an emergency production plant visit.
I’m female and so is my officemate. We’re both at home and I’m certain there are zero shoes currently in our office.
None under my desk. I keep them in a filing cabinet–13 pair. I refer to it as “my fine shoe collection.”