iPhones are all locked up, so ifixit's advice is worse than useless... it just serves to frustrate. What use is telling people to open up an iPhone when regular people don't have the tools to do so?
It might sound like a racket to you, but at this point they've saved me something like half a grand net, minimum, on phone repair and replacement, by making it possible for me to do that work myself and thus not have to replace phones nearly so often.
Most recently, this came in useful when I actually did drop a phone in water, just like we're talking about here, and was able to not only clean it out but also replace the battery, which swelled quite alarmingly in the aftermath.
The phone I dropped in the sink had a compromised seal due to a prior drop that bent in a corner of the case - something I did actually have the tool to fix, but hadn't got to actually fixing before the drop, thinking I had time. Of course, I thought I didn't need screen protectors either, until I dropped a phone and broke a screen for the lack of one - so, while I'm apparently pretty good at learning to fix phones, my ability to learn from experience may need improvement. It was the damaged seal that let in enough water to compromise the battery, but even so it stayed working long enough for me to pull a backup before I shut it down and took it apart. They're tougher than their size and cost make them seem, and these are just 1st-gen iPhone SEs - I expect the newer ones with glued-in displays are better still at preventing moisture ingress.
(Glued-in screens are harder to work on, but not impossible; I've fixed a phone with one, for a friend. You just need a heat gun and a lot of patience, is all. Regluing a new display seems like it'd be the hardest part; my friend just needed it working enough for data recovery, but maybe next time I'll get to find out.)
If he has the phone laying around still, you could practice putting the screen back. This way when you need to do so on another phone in the future then you already know how to do it :D