The only treatment method I know of is gradual, controlled exposure to what you fear, in this case, spiders.
Do you know someone who has a pet tarantula? You could have them bring it over. Start off by having it in a see-through container, where it can’t escape, and just watch it move, eat, and do its spiderly thing. Do this for, say, 15 minutes, for a week, or however long it takes you to become comfortable with the spider being there, in its cage. Next, have the handler take the spider out and handle it in the same room as you, but from a distance. After you get used to that, you can have the spider brought closer.
With each progressive step, the spider will be brought closer to you, and each time, you don’t progress further until you’re totally comfortable with the spider at that level of closeness. You don’t ever need to actually touch the critter. The point of the exercise, though, is to get to the point where seeing a spider doesn’t evoke the reaction it does now.
If that’s not possible… I dunno, maybe a book on spiders, with pictures, would do? You could have someone who doesn’t share your phobia pick a picture (one not too scary) and have it open in, say, your garage. Someplace you’ll see it, but not constantly. After a week, or however long it takes you to get used to it, you could place the book in a different room, in an area you spend more time in. I’m not sure this’ll be as effective as dealing with a real, live spider, but if you don’t have access to one, it’s the best you can do.