I can't think of any reptiles that I'd be phobic of, but I still wouldn't want to get bit by a bunch.
A lot of people seem to be nervous about deep water. I grew up on the east cost and we swam across the channel in the bay near my house (80 feet deep) and it's like you can feel the depth beneath you. I was always nervous in the back of my mind that a shark would come along, but what kind of shark would be found in those waters right? Then they caught the largest great white shark on record in those waters when I was 11. D'oh!
(if interested just do a search for PEI, great white, 1983)