My life is too complex for a dumb phone. I want TWO phones! One smart and fully featured (iPhone) and one dumb with just essential communication (phone/text). One telephone number, rings on both - is that so hard? I guess maybe with a "virtual" telephone this might be possible but those are increasingly not allowed IRL.
I actually find the smaller sized Apple Watch fills this exact need nicely. Screen is too small to leverage much beyond phone and text. Can leave the phone at home and still use the same number. Lightweight maps there if you need it in a pinch.
Not sure why this is downvoted it's a common opinion and one I've also thought about a lot.
I am actually about to do it, I think it's actually trivially easy if you give up on the phone number being the same for voice calls. If you have two iPhones then you can still get iMessage on both. And like who needs voice calls. If you really care you could forward one to the other.
The "dumb" one you set up MDM on and disable the browser if you want to really mean it. Just have text messaging, Kindle, spotify/music, and google maps. Seems like a decent compromise.