Phobias are created by our Reptilian Complex  this is an early part of our evolutionry brain thats primary objective is to protect us and help us survive. This is all well and good when you have learnt not to put your hands into a flame, or avoid things with sharp large teeth. The problem is, that this wonderful system isnt by any means full proof, infact it gets it wrong quite spectactually. So rather than the previous examples we can have a fear that logically we know we dont need. Unfortunately, its not that easy just to use your logical brain to bargain with this part of the brain.