Indeed--waterproof cases and well-rated waterproof cameras are great on the playa!
I don't have a waterproof case for my present phone, but used a plastic sandwich bag . . . which makes a certain number of people--both civilian and undercover--look at me eagerly on Burn Night for exactly .5 seconds.
IT'S JUST A PHONE.
Word to the neophytes: I highly recommend placing a sticker on your phone with your name, camp name & address (sometimes determined or perfected after arrival), your email and maybe a friend's cell number in fine point sharpie. That way, you might get your phone back during the event if someone turns it into Playa Info. If you don't want to make a sticker, you can have an image of your contact info on your Lock Screen, although if your phone is dead when you lose it, or the finder doesn't have a charger that fits, you will obviously be separated from your phone for a longer period of time.