Sorry to hear about your phone. At least you didn't have it long to become sentimental about it! Seems to me the love I have for the iPhone is for the species, not really an individual iPhone, although I suppose that with time..
Here's the deal with water and electronics in general, leaving aside the toilet diver.
The water itself won't necessarily damage anything, at least not right away (see further). In fact, electronic items are routinely washed when being refurbed or restored. The very one thing one doesn't do is plug it in "to see if it still works." If it is dried thoroughly, it may well work - but any energized components may be ruined - it would help greatly if the item were turned off, obviously. With modern stuff like iPhone, this may not matter, unfortunately.
One surprising thing about modern electronics is just how silly some of their vulnerabilities are. I can envision iPhone or similar competitors products with rubberized, shock-proof grips and exterior, controls and at least water-resistant (like our unfortunate toilet diver) enough to take a splash or two without complaint.
Anyway, from electronics sources I have read, most equipment that is
thoroughly dried will make it OK after dunking, but residual salts and calcium ions from fresh water will tend to cause problems or corrosion after a time.
Usually the advice centers around soaking the afflicted device in a suitably sized container of distilled water, sometimes first prefaced with an acetone/water/alcohol/detergent mix.
After that, thoroughly flushed with distilled water and dried. The US Navy, as one might understand, has addressed this type problem for a long time, I'm sure there is a manual somewhere on this kind of rescue. As someone mentioned the iPhone is problematic because the battery is not easily removable, nor is the back.
If you drop your iPhone in the lake, you could at least try
removing the battery, assuming the back is user-removable. What's to lose, if you can't get iphone replaced? LCD may not take extended soakings, but I would definitely flush the innards quickly but thoroughly and then dry in a controlled environment i.e. very "slow oven". Should be fine, assuming the always-hot battery doesn't torch a component while swimming.