Is there good screen time and bad screen time? For example, suppose I'm the type to have my nose buried in a book for 8 hours straight until the book is done. Or suppose I'm the type that is always reading a book and spend 3 hours a day reading. Now, instead of it being paper, its a e ink reader. Now, instead of that, its koreader on my phone. Does being a bookworm become a bad thing just because it's done with a phone?

Suppose you never use a phone, but you spend all your free time watching Netflix or playing diabolo 3. Are you better off than a phone user?

I think ultimately it matters what you do with your phone. Are you scrolling Facebook or reddit? You've probably gone past the peak of the value in doing that many hours (or years) ago. Are you video chatting with loved ones? Not as good as being in a room with them, but still not a bad thing to be doing. Are you reading scientific papers and discussing pure mathematics on a mathematicians forum? Are you spreading valuable information to people who need it?

I think, the only thing that makes a desktop better than a phone is that you can write code on it. You can be more productive. Beyond that they're just tools, what you spend your time doing is what's important.