First of all, I suggest you get treatment for your phobia so that you don't have to continue being terrorized by it. That's he long-term solution.

Short term, how would you feel about letting other teachers, and the principal, know about your phobia, how severe it is, that way you can all come up with a plan...... should one of your students vomit in your class, you'll call the office or the teacher in the next classroom, and they'll come in and take care of things. Is that a possiblity? If you let them know you're in treatment and doing your best to get a handle on your condition, I'm sure they'll be even more supportive.