There are some nice "minimal" launchers out there that restrict you to essentially a phone, camera, and messaging app. It adds a hurdle to accessing the apps that are easy to waste time in.

While now 100% the same as this, I've found introducing some extra friction can go a long way in curbing unwanted behaviors

I'm looking for something that asks me what I want to do before letting me open any app on the phone. Then it could periodically ask if I have accomplished my goal. "You have been "reading hacker news" for 30 minutes, are you still "reading hacker news"? [No] [Yes- turns off phone]"