You have to accept something: 95% of jobs involve social interaction on a regular basis. I had a hard time accepting that in the past, which led to failure and quitting.
This is important. Most jobs will require social interaction - when you get down to it, among those jobs, being a cashier is rather easy. But nevertheless, if you're looking for a job and having trouble doing so, you can't be picky about it or you won't get a job - beggars can't be choosers, and this is what I faced for well over a year of constant job-searching. It's possible, I'll tell you that, but I'll also acknowledge, that it is seriously difficult.
Chances are, you'll get used to the required social interaction for the most part - at the very least, you'll learn how to put up a good facade and make it look like you're handling socializing well. It's not something that in itself will remove your social phobia, but it certainly helps. I'm working at a fast-food/coffee-shop kind of store, and it can get difficult because it requires doing everything - being the cashier, drive-thru order taking (ouch), preparing everything, etc... at first it's difficult, but after a while, you'll adapt.
So if there's any advice I can offer, it's to just apply for almost every job you can apply for - using common sense of course, apply for jobs you may not necessarily like, but you don't need to apply for jobs you're going to downright loathe and everything. Or, don't apply for jobs you
know you are not suited for at all.. (Example: Fast-food may not sound too fun, but try anyways. But if you're oblivious/uninterested in fashion, don't apply for a clothing store.) Unless it's something you know would completely hate more than anything else, apply for almost everything.
Don't worry about the socializing aspect, it will handle itself. Employers, upon hiring someone, tend to be patient here because with most people, it takes some time for them to ease into working normally.