Camp is a good start. For what it's worth, one state in Australia just announced a ban on phones during school hours - couldn't agree more.
https://www.abc.net.au/news/2019-06-25/victoria-to-ban-mobil...
I think we should think holistically, this means, don't only look at school but also at family, peer relations and society at large.
In other words I propose that we should completely forbid functional smart phones for children below 10 years then officially introduce smart phones in school as a part of the school's curriculum. The curriculum also limits usage and relaxes the rules when the children get older. Children also should have a say about rules.
Also needed are places where children and teenagers can meet and these places must be autonomously accessible (for example near the school but independent from school).
Such a community allows the children to learn about internet and social media in a safe and controlled manner. I think the children would prefer to play together instead of staying alone in bedrooms anyway.