A smartphone and a book are, by and large, different modes of escape with different impacts on the escapee. Scrolling through social media is a far cry from focusing on a single subject for an extended period of time, which is what reading a book does.
Both are forms of escape. That can be escaping common boredom to pass the time, or it can be escaping bad feelings or a bad life situation. Also, I'm not convinced that a compelling fiction book that's struck a chord is actually a meaningfully different dopamine drip than scrolling Instagram.
Totally! But then you've got to make sure all notifications are turned off from every app that might hit you up - not just silenced, but so that they don't even appear over top of the book. And then, of course, there's the temptation to swipe over to a different app that's right there.