Kind of a non-sequitor, but there is one specific tool that has helped me break out of my smartphone addiction: books! The process is simple:

1. Leave phone somewhere not in my pocket and not within reach 2. Always have a book handy in my free time.

At least in my case, reaching for and reading my phone happens pre-cognition. It's completely automatic. I've found that I enjoy reading just as much, but unless I plan for it I don't have a book in reach. So the solution has been pretty simple: keep a book in reach!

Highly recommend.