I started by eliminating social media accounts, which had an immediate and positive effect on my phone use.
Next, I set hard phone time/day limits: no phone while hiking, no phone while at a social meetup or restaurant, no phone while shopping.
Finally, I focused on what I should use it for and stuck to only that: checking work email when I need to away from a PC (but replies wait until I get to a PC), the odd Googling when I'm away from a PC, scrolling my tech news feeds once per evening for up to 20 minutes, and of course, missed phone calls/texts from friends and family (checked periodically, 1-2 times per day).
And the end result? I'm very happy with my relationship with this non-invasive piece of technology, mainly because I ensured it was non-invasive.