The only real benefit of a waterproof phone, is not having to worry about it breaking if you ever drop it into water.
Rain wouldn't really affect a waterproof phone any less than a normal one. Those random splashes will however all be registered as button presses and make it really hard to use.
Thus you also won't actively try to use a phone whilst swimming since it would be annoying. Using it on a fishing trip (or whilst kayaking/canoeing) would still be just as risky.
The only thing you're going gain from having a waterproof phone, is the ability to take that one really nice underwater photo.
Since most newer smartphones are waterproof, to a certain degree, I wouldn't recommend choosing a phone based on how waterproof it is. It's just not really necessary.