The short answer is yes, numerous people put their phones in a pouch that hangs around their neck and then they can go into the water. The technology is advanced enough that these things really work, and the good ones you can even still continue to use in the pouch (i.e. take underwater photos, etc). This is the one I ordered, and I noticed that many others had as well. Plus they sold them at the gift shop (different brand):
https: //www.amazon.com/ dp/B0BTJ68LSC?ref=ppx_yo2ov_dt_b_fed_asin_title
(ETA - the url keeps showing up wonky so I'm separating it above)
I will add that this is not a totally new concept... I also still had some similar fanny pack pouches I had purchased 15-20 years ago for a cruise. I was never brave enough to use them, but I put my phone in my phone pouch and then in the fanny pack and I was able to go on the waterslides that way. My spouse really does not like heat/outside/waterparks, so this was the first time I was the only adult so I couldn't just leave my phone (and other belongings) with him. They do have lockers, but in the end, we just left most stuff at the cabana (most people do.. yes it's a risk but 99.9% of people at waterparks paid to enjoy the waterpark, not steal other people's stuff that they would then have to carry around).
I'm sort of responding to subsequent posts as well - the reality is, cell phones are a borderline necessity for survival these days in the U.S. I can't remember the last time I saw a working payphone (and I used them as a kid). We do still have a landline but people look at us like we have two heads when we tell them that. They really are your lifeline if you get lost, have an emergency, need info, need to contact someone, etc, because so many of the old ways of dealing with this stuff are just no longer in existence. And ngl, in this instance, I was with two kids, one of whom was not mine, 2-3 hours away from home, so some precaution is in order there.