Going back a decade or so, I bought a Yotaphone 2, which had a full-sized e-ink display on the rear. Fantastic for any text reading/writing in bright sunlight (I was based in Sydney at the time). Yotaphone is now dead, but I really don't understand why the idea hasn't been taken up by other makers.

Review (overly lengthy) from 2014: https://www.expertreviews.co.uk/technology/phones/yotaphone-...