Disable all social media apps if you can't actually delete them.
Turn off all notifications apart from calls and text messages (that way you look at it when you choose, not when it demands).
Switch off and leave in another room.
Get other devices e.g. a real watch, a standalone camera, an actual satnav, a proper stopwatch/timer, a real torch etc etc rather than relying on your phone for these things.
Have your photos printed out so you can look through them and hold them physically rather than mindlessly swiping on the phone.
If you have them, disconnect things like hive or whatever and use the actual, physical light switch rather than your phone. If you don't, don't get them. They're a bit pointless anyway, really, and will just further feed your smartphone habbit.
Find a hobby that will occupy your hands and your mind so you're not bored.
Turn off your Wi-Fi or set a timer for it to only be on at certain times in the day. Turn off your mobile data too.