There's a few reasons. You have to be aware that you're sinking time into your phone, realise that it is a problem and then exercise constant vigilance to keep

There's a few reasons. You have to be aware that you're sinking time into your phone, realise that it is a problem and then exercise constant vigilance to keep from falling back into old habits, comparable to many other addictions. There's armies of marketers and psychologists working to try and glue your eyeballs to your screen and resisting that pull is non trivial for many. A dumb phone and a dedicated GPS unit along with a paper calendar works well for me during times when I feel like unplugging; no self control required.