My favorite Dr. Phlox appearance was right around the same time as Star Trek: Enterprise. He got clocked with a frying pan by his long-suffering wife in one of the Six Feet Under opening sequences.
Looking at his IMDB page, he also shows up in the new Twin Peaks, as “Doctor Ben.”
They put him to great use on Leverage, as a no-nonsense head of security crisply pitting his attention-to-detail skills against otherwise-amazing art thieves who keep finding their plans foiled; recounting the story years later, those professional criminals reluctantly conclude that, man, that guy was so shrewd an operator that he might be smarter than the planner who currently masterminds their heists.
Spoiler alert: we then get to see why they cast John Billingsley in the role.
… And at least one episode of Happy Days,* too. 
*The only one I ever watched.
I rewatched the entire run of Frasier recently and I was surprised at how many Trek people turned up in that show:
Still finishing up The Mentalist. John DeLancie just showed up.
Next episode Mark Harelik.
It’s almost like an early Hollywood studio system at work here.
As a little side track here, I sometimes “have an ear” for voices.
In the recently released XCOM 2: War of the Chosen DLC/expansion, some TNG alumni have done some voice acting work:
Denise Crosby, John De Lancie, Michael Dorn, Jonathan Frakes, Marina Sirtis. 
The 1960s Tarzan series, starring Ron Ely as the apeman, is on Saturday mornings on the Heroes and Icons channel. Nichelle Nichols was in a two-parter called “Tarzan’s Deadly Silence.” And William Marshall (Dr. Richard Daystrom) has been in a couple episodes.
Another TOS–Batman crossover: Joan Collins (“Edith Keeler” and “The Siren”).
Nichelle Nichols in this cinematic masterpiece.
I believe Netflix still has it on disc. We actually watched it because a friend of ours is one of the principal characters.
This one too:
James Doohan died on screen in The Satan Bug, released in 1965. I don’t think he had any dialog. Creepy death scene, well acted.
Cool! Alistair MacLean is one of my favorite authors. I do not recall how faithfully the film followed the book. I do recall Richard Basehart as the bad guy.
He was also in an episode of Marcus Welby, MD with hippie sideburns and a hot (Asian female) dinner date.
Big wire-rimmed glasses, too. Very '70s.
I think I first saw him in a low-budget PBS TV movie about Fort Necessity and the French and Indian War. He was pretty good as a young George Washington.
She was on Cheers a few times too, I think, and played Mrs. Columbo on Kate Loves A Mystery.
He was good as a gruff but beloved soccer coach in The Damned United.
I remember seeing him in the early Seventies in an educational film about choosing the right career. It would’ve been only a few years after his first Star Trek run, and he was very good in it.
Well, he had played a guy named Jesus before…: King of Kings (1961 film) - Wikipedia
He was also in John Candy’s last (and critically-panned) film, Wagons East!
Takei was also in a movie whose name escapes me at the moment. He played the commandant of a Japanese POW camp who was tried and hung after the war for his maltreatment of Australian prisoners.
Wasn’t this the incident where Washington bushwhacked a French contingent looking to parley? Ouch! :smack:
Accounts differ, but yes: Have we ever had a killer in the White House? - The Straight Dope
Wow. Takei was in a camp in Rohwer, Arkansas during WWII.
Penny Johnson Jerald, who played Kasidy Yates on Star Trek: Deep Space Nine, is now playing Dr. Claire Finn in The Orville, a new Seth McFarlane sci-fi comedy. It debuted last night, and I enjoyed it.