How to get over a phobia?

I think I need some advice with this latest problem! The snake this has gotten worse… he does not want to use the toilet by himself… he needs us to go with him, and if we can’t, he starts to cry… actually scream! And he says that he is afraid of the snakes in there.

I am really stumped on how to deal with this one… I try to assure him that there are no snakes in the house, and that we are safe, but it really does not seem to be helping.