I don’t like the idea of rules being set by people who don’t know individual children. I wouldn’t be happy if mine had been on screens for 5 hours a day, but neither would I like someone outside of the family setting rules for my household. My children were teenagers when smartphones came in and data was too expensive for them to be on them for hours, but I do remember people saying there should be rules about PlayStation use and so on, and that their rules should be enforced for everyone.
I briefly tried to legislate about that at home, but soon realised that the children regulated themselves- they would play for a while then go out and play football or find something else to do without my interference, which they resented, as they knew what was fair, who needed another turn and so on, and I didn’t. Learning to do that was far more valuable than having someone standing over them pointing at her watch, with only a vague idea of what was going on.
I agree that banning phones is intrusive and IMO is outside the remit of anyone other than parents. By all means ban their use at school and penalise misuse of social media, bullying and so on, but if it works for a family to be able to contact one another they should be able to do that. Phones can be switched off during school hours but it should be up to parents if their children carry them to and fro.