It seems more like he was watching educational videos on YouTube before getting a phone, and has since become addicted to other phone things?

Parents always worry like this. Mine used to worry I was "addicted" to programming on the home PC. I'd say, no mum. I don't go outside and frolic in the fields like a Victorian-era child because we live in the middle of a giant housing estate in the North West of England where it's always cold and pissing with rain. My friends live a car drive away and we aren't into football, which is the only thing available to do outside around here, plus I read most of the interesting books in the house already, I've grown out of cartoons, the computer is more interesting than children's TV and definitely more interesting than homework, most of which is of obviously marginal utility when I become an adult.

Or at least that's what I would have said, if I'd been articulate enough to know how.

The child in this article doesn't sound "addicted" to her phone. It sounds like the wealth of social, creative and interesting activities available through it are just far more interesting than playing dolls with her mum. Maybe it's tough for her mum to accept that her daughter is growing up, but she had to grow out of that at some point - it was inevitable that something would replace it. Would she prefer if it had been TV, like it was for prior generations?

Yes. Addicted to Twitter, instagram etc.