I don't understand why people have to downgrade to a "dumbphone," other than joining a fad or trying to put attention to themselves.
One can use a smartphone without any of the "smart," and it will still be a great phone. Just activate the iPhone and don't download any apps. Put all built-in apps into a folder and just put phone and messages app outside the folder. Then disable data and/or notifications. Done. Compared to a dumbphone, you will still enjoy the great camera, music listening, better contacts navigation, all the stuff Steve Jobs said on the original iPhone. Better and easier to use phone. Simple as that. And you'll find without apps and data, the battery life will greatly increase.
The iPhone is just a device. It's up to us how we want to use it. Letting a thing controls you is silly, and people going back to dumbphones are just attention seekers.