A simple first step, which changed a lot for me: Keeping your phone on Do Not Disturb permanently.
It (AT LEAST) frees you to decide when to check the phone, rather than letting these companies, (through notifications) decide for you when you're going to check your phone.
Another benefit of this (at least on Android) is that you can set Do Not Disturb to "Priority Only" and have it allow calls/texts from your contacts, but not other notifications. This eliminates telemarketer robocalls, as they're very unlikely to get lucky and spoof a contact's number.
I also turn off the ability of most apps to display notifications. That helps.
Yep, you can do the same with iOS too with allowing contacts to get through. I turn off all notifications entirely is my first tip, at least to not be on the home screen. I have to actively want to look at notifications, push notifications are almost sheer evil.
Second is to restrict your internet use to specific times or to just say an hour every night from 9-10pm. Lets say start out by saying internet only from 0-15 minutes on the hour (initially). The idea is to get you used to not reflexively use the internet to prevent boredom or distraction.
How you accomplish that, say by killing your internal dns server to not respond or even firewall off your network from reaching the internet is up to you. But the key is to make it so you change your habit of when using the internet is ok.
Oh also, leave the phone at your desk, only pick it up when you need to look at it or if it rings etc...
Another good tip, reward yourself for each milestone, you want to encourage yourself to do the right thing. Don't use negative reinforcement unless you really know how to make that work. Its easier to do stuff like: if I don't go online at all today, I'll eat a container of ice cream (bad example if you do this every day but you get the gist) as a reward.
And once it's in DND mode, I trained myself to only unlock the phone when I saw a notification.
I still pull the phone out of my pocket several times an hour, but a quick push of the home-button and a confirmation that there's nothing of interest leads to it going straight back into the pocket. It's liberating!
Step 2 was removing the browser shortcut from the main screen, so there's less temptation to just 'fire it up and check HN quickly'.
having a smart watch eliminated even that for me. they’re pretty fantastic triage devices (deciding what to ignore rather than making sure you’re instantly aware). i barely ever check my notifications any more. i see friends at cafes pull out their phones every few minutes and get distracted by facebook, but i’m quite content to have it just sitting on the table because i know it’s not doing anything
It (AT LEAST) frees you to decide when to check the phone, rather than letting these companies, (through notifications) decide for you when you're going to check your phone.