That's a difficult one since phobia's are all in the mind. First of all if you do watch horrors, lay off the clown ones as an obvious statement. You need to try and get into a mind set that whatever phobia it is, it won't hurt you. Clowns for me are birthday party, balloon twisting, colourful characters but having phobia's myself I can understand what might run through your mind.
I try and picture something funny when I see something that scares me. Try it, you never know...