> I wish they'd just confiscate them and only return them to the parents, or have some sort of phone not allowed without good reason (and revoke it if someone breaks the rules), but they seem averse to that kind of thing.

A lot of parents will throw a fit if schools try to take them away or ban them, and, contrary to public perception in some circles, public schools really hate upsetting parents. It's part of why private schools tend to have a lot more success enforcing phone-related rules or restrictions, since they can just tell a family to pound sand if they don't like it (they all have waiting lists anyway, if you're not some huge donor they don't need to give a shit what you think if it's not in-line with their approach and mission)