Hello there, What's the difference between the two sentences:"I'll go unless he phones first,"and I Won't go unless he phones fisrt."THANK YOU.

Unless you wanted the Haitian Creole grammar for these sentences, I think this is a question for  English teacher - Not a Haitian Creole teacher.
But I'll think you what I think anyway :)
The second sentence makes sense.  The first one seems unfinished.

I'll go, unless he phones first (then I won't go?)
Mwen va ale, men si l telefone anvan sa (mwen pa prale?)

I won't go unless he phones first. (Basically: If he calls I will go. But if he doesn't call, then I guess I will not go :)
Toutotan li pa telefone mwen pa prale.

Haitian Creole ↔ English Reference, Look up Haitian Creole and English Words