Decent device to convert a smartphone in to a tablet?

I’m asking for a friend. I know a elderly person who loves his smartphone but sometimes the screen is just to small for him. He allready owns a tablet and a notebook and he hates both of them.

He hates them because the interfaces are different and he has to maintain logins on each device. https://showbox.tools/

I have found the pricy ASUS ZenScreen MB16AC (missing touch). Are there any cheaper options to just have a larger screen?