A flip phone/dumbphone would sort of be mutually exclusive with my use case. I use my smartphone nearly exclusively as a lightweight mobile computer for web browsing, SSHing into my server, and messaging over internet (not SMS). I rarely use the “phone” features of my phone, i.e. phone calls and SMS. So I’d be losing out over the features I do use, in favour of features I don’t use.

If you’re being distracted by your phone and a dumbphone works for you, good on you. I think most people are like me and use their phones as a small mobile computer rather than a phone though, in which case distractions are best handled with one of the many apps/browser add-ons/etc that block websites or apps.