If the kid is old enough to need a phone, they're old enough to be a caddy or babysitter or something legal for kids to do and buy it themselves. You don't have to facilitate the purchase.
I think there's a strong class component to it, too.
I've got kids in public schools and one in a slightly-fancy private school.
The public school kids all get phones super-early and are prone to mocking kids for "being poor" over stupid shit like not having a phone (one of mine was so-mocked for "only having one backpack"—JFC, was Fussell ever right to shit on the class-anxious, pitiful, absurd Middle, give me "High Prole" over that crap any day).
Meanwhile, the private school kids whose parents are doctors and attorneys and VPs and related to major local politicians, get phones later and don't regard them as a status symbol. Phone ownership rate is maybe 50% by 7th grade, while I'd say it's that high (maybe higher?) by 4th or 5th in the public schools, and more like 95% by 7th. The private school also has much stricter rules about phone use during school (I gather all the area public schools have totally given up on stopping all but the most egregious use of them in class, as the parents who gave the kids the phones won't back them on enforcing anti-phone rules, and will in fact throw tantrums over any such enforcement)