What I want is a dock I can put my smartphone into and then the old phone interface takes over. Preferably one with links to 1-2 other docks in the house so all three ring if I get a call.
Pick up the physical receiver, say hello. Talk. Say goodbye, hangup. No screen interaction at all.
Mine is an older Panasonic system, but I'd be surprised if other manufacturers didn't offer something similar.
Though, (and I should have mentioned this in my original comment, sorry) I've never actually used the functionality in question, so I don't know how well it actually works.
Ever since switching to a phone/tablet though, (Android, in my case), I now have to first locate the phone, make sure it's oriented right-side up, attempt to remember which direction I'm supposed to swipe, and if I can't remember, attempt to decipher the tiny symbols without any explanatory text.
I remember at one point that the entire UI changed when I upgraded Android and the next day I could only stare blankly at the screen trying to figure out what was going on while the alarm blared in my face.