This is stupid. There is no better time to use your phone than when taking a shit.
For years, that was the only context in which I read Twitter, and that still holds true today for the various things that replaced Twitter for me.
The toilet is a fine place to peruse this website, too. It's pretty hard to do anything to excess if you only do it there.
Instead of trying to be present and think valuable thoughts while shitting, I recommend doing that while not shitting.
Make a habit of taking walks. Maybe learn to do mindfulness meditation. Clean the kitchen in silence.
There are really a lot of better options than locking yourself in a small room with only your thoughts and your feces.