I like this idea, but lack of encrypted messaging (Signal/Matrix) makes this a no-go for me.

I second the recommendation of GrapheneOS to at least prevent some of the tracking.

Having a simpler phone would be great, but a good second choice is to limit what apps you install so you have less distractions available.

There have been several times where I've picked up my phone because I'm slightly bored, stared at the home screen for a few moments, and put it back down after nothing grabs me. After that happened a few times, I've started reaching for my phone less often.