It's pretty simple. For example I may say the person above me has hippopotomonstrosesquippedaliophobia (The fear of long words.) Pretty ironic, isn't it? In case you need help: http://phobialist.com
Now you've got me wondering what that show was that I watched at one point where some kid got a new mirror in his room and he didn't like it and his reflection moved on its own and grabbed him and took his place. I'm not, but that show did stay in my mind for a bit afterwards. Hmm... I wonder what that show was called again... I think it was quite an old show or something as I remember them showing it on "retro week" or something like that. Bet it scared quite a few kids that show. For the poster above: Perhaps a fear of mice? Pure guessing here.