Turn off all notifications except SMS and phone. Change email to pull, not push. Delete all social media apps, use the phone browser for it. Remove all work applications from your phone. Either you’re working or you’re not, no in between where you get pulled in against your will (I have a work phone provided by my company, so it’s easier).

I did this 8 years ago and I can’t recall anything important that I have missed. I can still look at email/social media/whatever in the browser or I sit down at my tablet/laptop. I still have Spotify and YouTube on my phone, but I try to limit entertainment apps on it.