When you are reading a book, you certainly need to use your attention. However, you stay in a given topic/world for a sustained amount of time. This feels very different and much less tiring than scrolling on your phone jumping from topic to topic. Especially social media feeds that have been optimized to keep using it as long as possible (dopamine hits and all).

Newspapers are probably an intermediate between those two, to various degrees depending on the specific newspaper (trash vs deeper analysis).

I think it can. In extreme cases (say grad school) I've had books and "book learnin'" suck the life out of my life.

"All I can do is read a book to stay awake And it rips my mind away but it's a great escape." - Blind Melon

A smartphone, at least with a connection to the internet, is always new. There is always something new to see and hear.

Yes, but you tend to carry around a smartphone all the time and the temptation to whip it out whenever there's more than a 5s window can be very strong.

The both have an end and limited novelty.