I'm Gen Z and was not allowed a smartphone until I was 16 (primarily because my mother was worried her estranged & abusive ex would use it to stalk me) I was furious with her about this for ages & it did cause some difficulties but ultimately I'm grateful I didn't have one. A lot of drama & upset at my school seemed to be fuelled by WhatsApp, among other issues I've seen SM cause among my friends and wider peer group.
I know it's extremely hard especially when all other children have them...what was needed was a collective effort. If smartphones had never been allowed for under 16s, I think the current explosion in mental health issues, and related issues like online misogyny and ROGD would be far weaker.