The iPhone is waterproof and you can take a photo with the physical volume up/down key. I've used it underwater a couple of times, none of my other proper cameras would be able to do that. My two cents.
One other thing I do like about the TG4, nice big buttons, and I've had plenty of opportunities to use it in rather adverse conditions.
Asking for a me who doesn't want to fuck up a thousand euro phone trying something stupid next time I'm at the seaside :)
https://support.apple.com/en-us/HT207043
"Splash, water, and dust resistance are not permanent conditions and resistance might decrease as a result of normal wear. Liquid damage is not covered under warranty, but you might have rights under consumer law."
I think of it more as good to have for an accidental drop, rather than a specification to rely upon for regular underwater photography, although the more recent phones do reach ever higher Ingress Protection (IP67, IP68 etc) water/splash/dust ratings.
They are water resistant, but I wouldn't use it in water as a matter of course. Maybe if its in pristine/as new condition, at best - I've dropped mine a few times, which probably didn't help.