What do people do mostly on their phones? Browse internet without any real aim, usually, like browsing reddit for example.

What do you do when you read a book or similar lengthy piece of text that requires to think about it? You're focusing on one subject, whatever it might be.

What does browsing internet aimlessly cause? It enforces habits where your brain tells you that you should browse internet aimlessly when you dont know what else to do. Problem is, you start doing this all the time. It encourages procrastination as an habit. Sure, not a problem when you actually dont need to do anything else or are waiting or whatever, but when it starts to become deeply rooted habit, you will be looking your phone all the time, unable to focus for example on doing homework that could be done in 30 minutes, instead you use 1,5 hours to it because you cant stop checking your phone all the time because you feel this nudge in your brain telling you that you need to check that phone even though there's absolutely no reason to.

Reading a book in other hand teaches focus and concentration. I dont need to explain why those traits are good for every single person.

Not saying this happens to everyone or even a large portion of smartphone using population, nor saying that smart phones are cancer or something, but it's just something that's happening.

Not saying I'm right though, but it worries me. I work in a school environment and have seen and heard somewhat plenty on the subject but can only draw semi-biased conclusions based on those bits of real life experience and random studies that I've read somewhere sometime.