Interesting 'ban smart phones' bandwagon middle class parents are currently jumping on.
There are social media groups with hundreds of parents and teachers and other ransomers discussing the perils of high school pupils using phones. Some are in fact sharing screenshots and other content taken from their teenagers phones, thus violating the individuals' privacy and causing safeguarding issues.
Interestingly they are moaning about smart phones and social media- using their smart phones and social media.
Of course, as is the nature of such online groups, users work themselves into a frenzy, the loud and ignorant participants dominate and no sensible and nuanced discussion can really take place, oh the irony.
I am all for having phones out of sight, ideally handed in during school hours. But that's not sufficient. Schools need to include not sharing any offensive (racist, bigoted etc), violent or sexual content in whatever format, not just using phones. All schools have computers in fact most now hand out iPads to their students. It's a bit futile to ban smart phones but expect students to use their iPad for educational activities as it fosters screen addition and enables students to access inappropriate content. Brick phones are also addictive although perhaps to a lesser extent.
I advise the OP to campaign for a personal device free school and have a extended behaviour policy as well proactively creating a culture that teaches pupils responsible, safe and worthwhile behaviour online as well as offline.
Do not be tempted to wrap your dc in cotton wool, OP. Teach them to not watch stuff like that, teach them to say no and walk away, encourage them to have sound values around internet use. We cannot put the genie back in the bottle, but we can try to a culture that empowers young people to be as educated as they can be and have safe behaviours just as you'd want them to have in real / offline life.
The ban smartphones camping is simplistic and kind of just delays the problem. Away with the phones at school for sure but remember there are other devises at school that give kids internet access to look up and share or show inappropriate content. Otherwise just heavily control your dc's online behaviour, smart phone or not.