My parents gave me really shitty smartphones that were barely powerful enough to do important things but was an awful experience for Instagram/games/etc until I bought a better one with my own money (similar specs to Pinephone Pro)

No luck necessary. Not like you need permission from your child to deny them things.

You can get a dumb phone since having a phone (not necessarily smart) is a good idea. There's also parental controls on at least Android smartphones that let you control the apps and sites they get access to.