fyi a quick tip for some of us looking to trade old phones at Apple store... the 1st thing those Apple geniuses look for when inspecting phones is water damage indicators built into the phone, if indicators are on then trade in value is probably not gonna be good (they wouldn't take mine last time), so check those first and save yourself a trip.
if you are lucky and indicator is not active (or the phone bath was so brief that nothing got in), then also check the power/sync connection area if there is discoloration or hints/hues of green, that happens when the metal parts come into contact with water (saltwater is even worse) and get oxidized.... you can remove the greens with q-tip & alcohol... worked for me on an older iphone when trying to do a trade in.
I googled online and found many articles on iphone water damage indicators, here's a quick link to one:
https://www.gazelle.com/how-to/iphone/water-damage.
Good luck!