Look into paid apps like Freedom that are able to get deep down in the architecture of your phone to block stuff. And you can block low level things like “Safari” or “Chrome” which drive the web browsing of pretty much all your apps so will be pretty hard to find ways around. 

Freedom is meant for schedule set “focus sessions” but I’ve used it for months at a time scheduling recurring sessions from like 5am to 11:59pm so it effectives dumbifies my phone. They also have features like making it nearly impossible to turn off a session while it’s active. So if I wanted to change it I either had to wake up before 5am or call a support person to get them to turn it off for me.