I don't have any bathroom phobias. When I was young there was a commercial about a monster toilet (I think it was a toilet cleaner commercial) That freaked me out, and gave me an irrational fear.
https://www.youtube.com/watch?v=L5WULhUiYrc"]Tub Of Goo - YouTube Quite funny if you look at it in a certain way...
I don't like to have the shower curtain closed because I have a phobia of serial killers, and I figure behind the shower curtain would be a pretty decent place for a serial killer to hide. For the same reason big, empty public restrooms freak me out. Especially at rest stops. I used to have this thing when I was a kid where I had to leap out of the tub, dry off, get dressed, and make it down the hall to my bed before all the water drained out. For some reason I thought if I didn't make it to my bed in time a snake would come out of the drain and eat me. So I think I still have some residual bathroom trauma from that as well.
^rest stops on the interstate can have some pretty disgusting restrooms for sure, as well as some strange people, probably fugitives with multiple felony warrants for all sorts of heinous crimes;-)