For folks like that any kind of smartphone with "off-the-shelf" software is a non-starter-- too many options, too small, not tactile.
The problem with "dumb" flip-phones is that they tend to be small and slippery. An arthritic octogenarian will have a hard time even opening a flip phone.
The ones that are "designed" for old folks tend to be setup as "medical alert" devices-- a big red button on the back and all the drawbacks of a regular flip phone. They're more designed for paranoid family members than the actual users.
The phone I purchased for my octogenarian mother is an Alcatel "GO Flip". She has difficulty opening it and the buttons are too small. As a work around I programmed numbers "1","2","3","4" as a speed-dial to me and the rest as a speed dial to my brother. She knows to press "1" for me and "9" for my brother. I tell her to hold down the number until she sees my (or my brother's) picture. $75~ for the phone, $20/month for no-contract unlimited talk/text (she doesn't use text)-- that's it. That's the best I can do.