Most schools in the UK ban phones in school. The difference here is that in this study phones were taken away for 21 days, even after school. They lost access to the phone completely during that time.
I am less convinced that we should wholesale ban phones for kids, because in the UK at least, there is no longer any culture of letting kids go out and socialise. We need to provide spaces for kids to be kids, and safe.
However I do think social media use should be severely restricted, unfiltered video being zapped into young minds is not the way to build a cohesive society. tiktok/reels/youtube should probably be editorialised so that we can avoid the stupid, bullying and dangerous stuff being spread by arseholes.
Furthermore I think phone use should be time limited by default. That is, the default is that the phone stops all notifications after 20:00 apart from things like parents.
I have two kids, and I despair at other parents who think its fine to allow their 10/11 year olds to start group video calls at >20:30. Or the ones who let their kids bully on the class whatsapp.
Part of this is education, most of it is tech companies wanting to make money from kids (including mine.)