I think e ink is all you need in a hiking phone as long as it has a reasonable camera (or perhaps none at all) and can display maps and books well enough. The trade-off of not having to charge for say a month is enormous value.
This one weighs only 47 grams:https://www.e-ink-info.com/e-ink-devices/mobile-phones
HiSense A6 is a new smartphone with an E Ink screen: https://goodereader.com/blog/smartphones-2/hisense-a6-is-a-new-smartphone-with-an-e-ink-screen
This one’s main screen is e-ink (which probably means the battery will last you a month: https://www.pcmag.com/feature/313023/hands-on-with-the-onyx-boox-e-ink-smartphone/1
More about this when I get out of hospital!