I usually stay away from corporate gym and go to the local community gym. I have my own gym, but I miss the energy you get when others around are jazzed up training hard. I don't miss the steroids type bragging and trying to own the place. Not all of them do that, but most have done that.
The cell phone rule is because most cell phone have cameras and many gym put up warning, and if getting caught taking photo of someone, is punishable of one year in jail, but only if they post these rules. The gyms themselves can get sued if they failed to post these warning. I have seen a man climbing over a tanning booth stall trying to take a picture. The gym owner did press charge on that guy, but he end up going to jail for a bigger offense. He was wanted for a bank robbery and he wore his HS football jersey with his name on it. That's another story. Anyway, the tanning booth walls had many holes in it and every week I would patch the hole with filler paste. After that guy was arrested, I saw no more holes in the tanning booth wall.