My phobias are drowning and falling long distances to my death. I'm not afraid of deep water or heights in and of themselves, just the possibility of death involved in them, so I don't really consider myself to be afraid of heights or water in the traditional sense. It's more like subsets of a fear of dying than a fear of environmental factors.
The falling thing is no big deal, barely affects me. So long as there's no real risk of me actually falling to my death, I can go up to the top of a dozens of floors tall building and look down from the roof and be just fine. Put me on top of a 5 story tall building that has little to no railing around the edges and I'll stay way the fuck away from the edge because fuck that I don't wanna fall to my death. I'm fine with planes because I know there's such a ridiculously tiny chance of them crashing, but I'm not really comfortable with balconies that have short enough railings that I feel like a solid push would make me topple over them rather than stopping me.
My fear of drowning is the worse of the two. I'm okay with pools and other relatively shallow waters, shallow meaning that if I stand upright in them my head will be above water. I never learned to swim because whenever I get in deep-ish water and take my feet off the ground the fear of drowning kicks in hard and I go into fight or flight panic mode and it's just a bad time for everyone involved. Ironically, the thing that would probably alleviate my fear of drowning the most would be learning to swim, but I've never bothered to muster the fortitude to conquer my fear enough to learn because I figure that it's easier to just avoid drowning situations altogether as best I can instead of purposely putting myself in risky situations. I can hang out at the beach with no problem, because the vast body of water existing does not trouble me, but swimming out in the ocean or going on a boat into deep water? No thanks. I can tolerate the boat thing if extreme anti-drowning precautions are in play, like railings to prevent falling off plus the presence of seats with seatbelts just in case, but I'll wear a life vest at all times anyway and I'll probably be all nervous and uncomfortable the whole time. I absolutely won't swim (or wade, really) out very far into the ocean at all. Waist level depth is enough for me, then I'm done. I've heard way to many stories about sudden drop offs and riptides and such that I just don't want any part of it.