This. It's better to gradually introduce them instead of fully abstaining. They'll need them at some point, as our society is becoming increasingly reliant on it, and when you suddently let them do whatever without moderation, the same problems will occur.
not every parent has the time or experience to do that. banning smartphones is easier than constantly supervising their use. to much supervising may also breed resentment from the kids, especially when they get older.
i feel it's better to first deny them and later give them the phone on trust. like they are old enough to handle a phone now. that should lead to a better relationship with the kids