The old Nokia in school wasn't a problem. You get in trouble for playing snake. The iphone 1 wasn't really a problem. There weren't that many, and it served as a calendar.
But year after year, release after release, the industry deliberately loaded more and more addictive machinery, pushed more and more boundaries, until it's beyond unacceptable.
As an aside, it's amazing how hard it is to turn the modern phone into a no-nonsense tool, and I'm an adult with self-control, a deep understanding of dark patterns, and a fully-functioning brain after 3 cups of coffee.
They disappeared for a few years, but now you can buy a dumb phone, for example running KaiOS, that charges with USB-C and supports modern cell networks. You can even get a Nokia!
There is absolutely no need to buy a smartphone to any kid younger than 15. Now for high school students it's a bit different, they should be old enough to have self control and respect rules to keep their phones in their bags during class.