I feel like I am the only one but I am genuinely excited for fold out phones to become more robust and common as I feel they will solve a lot of problem for people with extended (tremors) / restricted mobility (arthritis) and make their interactions with their phones a lot easier.
In the meantime, I can talk about some design features I have seen within the software on the phones and supporting hardware which tries to help in this area.
External keyboards - I know. I know. They run over bluetooth, glitch, freeze and then we discover they have been trying to talk to the collar of the dog next door but if you don’t have the control to be able to manipulate the tiny smartphone keyboard, these are invaluable to have. Also good for us who are going short-sighted too.
Orientation - the ability to be able to landscape a phone and have the feature become bigger and easier to touch accurately is a blessing for motor based accessibility.
Zooming - no, not video calling, the OTHER zooming - focus. The ability to be able to zoom in on a feature to have its features increase in touchable area is a brilliant design feature. It started off a bit flakey in early android phones (the feature size scaled up but the touchable area did not ) but since about Android 6.0.1 Marshmallow, the touchable area has scaled with the feature. This is really good news and the right direction to be moving in.
Sensitivity adjustment - if you have extended mobility, having an over-sensitive touchscreen can lead you down some rabbit holes you do not want to go anywhere near so in order to combat this some phones allow you to adjust the touchscreen sensitivity.
Swipe adjustment - in a way, a lot of the same advantages of sensitivity adjustment above. If you are not able to manage single thumb / finger swipes and want to just use a double swipe for all (or vice versa), you can change this on your phone to make it work for you.
Options other than “the hand” - A lot of work was done on mobile phone use to identify where most people used the most phone areas. These were known as the thumb zones (i kid you not!) and companies paid £10000s in order do the research in order to understand the design for neuro-mobile “typical” folk. That thinking is gone now and the design thinking is how to get maximum amount of folk using devices. Understanding hand-based mobility issues are a huge part of that (hence the death of the single fingerprint login) - we now have password, eye-reader and voice unlock too.