As far a silly phobias, most of mine are incredibly silly (which I can admit), but they are almost debilitating for me and came about for legitimate reasons. The two that most readily come to mind are sparkalaphobia and gnomophobia.

When I was 10, I was making a card for my Mom and I had a couple of tubes of glitter on my bed. The green glitter tube inexplicably exploded and glitter was everywhere. I was still finding it in books, mattress folds, my bed sheets, etc... years afterward. I'm moving out soon, and I half expect to find more once we're all packed up (I'm 28 now). Ever since then, I hate the stuff and am extremely uncomfortable and get really panicky/upset if any gets on me. Every time I get a card or something, I have to ask my brother to open it just in case there's glitter on the card, and there almost always is.

As far as the gnomes, when I was 15, I went to Disney and went on the Spirit of Norway ride they had in EPCOT at the time. Scarred me for life (yet I went on 2 more times, because I apparently hate myself). I can't even look at garden gnomes. I have 2 exceptions to this, though; this and the Roaming Gnome, for some reason.