An activity in HS is not synonymous with an iPhone. An iPhone is a luxury that your kid doesn't need. HS activities, sports, social things that add to the resume of the kid when applying to college and learning that social aspect of life at the HS level is something completely different.
A kid should have something like that to keep them out of trouble, at the very least. And to form social bonds with their peers. Thats why those things are important, and continue to be - like I said, when applying to college and later in life.
How do you not get that?