Why are so many people turning to ‘dumbphones’?
theguardian.com
theguardian.com
So the actual problem is the lack of updates and lack of user freedom which can be provided with free software.
> But such is built-in obsolescence, pretty soon I’ll have to get a new phone.
Same as above. These problems are solved with GNU/Linux phones (Librem 5 and Pinephone) which run mainline Linux kernel and will receive lifetime updates.
Then you don't need a dumbphone either, you can also do that from a computer.