Triskadecaphobia-fear of the number 13
Fear of clowns
I think that most phobias aren't phobia's of individual things, i think the thing that terrifies people is being trapped or enclosed with something you don't like or are scared of. I think people can be scared of things, but the thing that's actually so sinister and frightening (and causes panic) about it is being in an enclosed space or being unable to get away from it.
I believe that most people develop phobias due to family life or the way they have been brought up. If a child is in a home where their parents are afraid of something they will naturally develop the same feelings towards it. Also, if children are abused or neglected they may also develop phobias, eg. claustrophobia or even a fear of open spaces because they might be so used to being inside all the time that when they finally do break out into the real world its such a shock.