I wish Apple would open up customization capabilities to properly kick the addictive elements from the phone, like Android with custom launchers...
I've also experimented with Apple Configurator many months ago but unfortunately it's too tedious for most people wanting to enforce a simplified phone, but its beauty is in its level of power of creating a bespoke iPhone experience.
fwiw I'm the maker of the Dumb Phone app (dp) that somebody mentioned below and what's mostly kept my daily average screen time to 1-2 hours is getting rid of the addictive elements from the home screen.
No more color, icons, fancy wallpapers, just a simple single-colored text-based list of my most essential apps that open when tapped. Zero social media.
We live in 2025 and as much as i'd love to experiment with a nerfed feature phone, I personally need a high quality camera each day, maps of course, banking apps, authenticators, etc.
Kicking that dopamine hit has helped me use my phone as a utility again, otherwise I put it away. I have an Apple Watch too with all alerts turned off except for calls, texts - so another reason to keep the phone down.
Since I also run a business I do need to leverage mobile social apps, so these now all live on a "separate" iPhone which stays in a drawer until I need to perform a particular task with it, then it goes back in right away.
Genuinely feels good to have my phones work for me now rather than the other way around, and I see a lot of common sentiment when I speak to people who have also done the same thing to their phones.
Highly recommend cleaning up your Home Screen as a good starting point, and purge your notifications.
edit: I also begrudgingly installed Beeper last week to keep in touch with an important group chat on FB messenger on the main phone, but it's bliss only seeing a list of group messages vs the long list of story buttons along the top in the main app, green and red dots, so i'm not inclined to tap around afterwards.