I feel like I'm reading a lot of defensive posts by parents who feel like they don't have much control over their child's phone use and try to paper over the cracks by telling themselves that their pre-pubescent children are sensible about screen time and that we live in a digital world so there's no point fighting against it.
There is a point fighting against it. I've seen it over and over again with my own dc and their friends. The kids who have phones in primary school have those phones glued to their hands non-stop. They don't know how to play at the park without filming themselves. They message random numbers of adults (my dd's 10yo friend recently messaged me at 8.30pm on a school night thinking it was my dd's number - she doesn't have a phone). They are part of whatsapp groups with unknown members who share inappropriate images - and nobody seems to know who these people are.... These are all primary aged children - the ones whose parents think they are sensible kids.
They are children, who are losing their chance at a childhood spent playing outdoors and learning social skills through face to face interactions. Instead they are all huddled around phones on the playground before and after school.
I know a woman who gave her 10yo a phone and she said it was like a switch flipped - her dd was outdoorsy and loved gymnastics, and quickly became obsessed with her phone and sitting in her room instead. She couldn't quite pull it back and has since given up trying to impose restrictions. It's really worrying and depressing, I've lived in several areas over the years and I see the same patterns over and over.
I was going to type more, but I think there's enough evidence to suggest a smart phone isn't a good idea for a pre-teen or young child, and that social media was never intended for under 16s to access. There are bad actors on the internet who are tirelessly pursuing ways to get into contact with other people's children. That in itself is enough to make me extremely wary...