> If you don't use a skill, that smo atrophies
I don't think the _ability_ to memorize phone numbers is what atrophied here by getting a cell phone. The _need_ did. It's harder to memorize phone numbers today because we lack the practical application of the memory (e.g. only when something fails do we actually try to put that memory to practice). I bet anyone would quickly pick up on memorizing phone numbers if they had to both remember and type in the phone numbers every time they wanted to make a call or text.
The ability atrophied because it was not practiced because there was no need.
Maybe as per usual, I think we all mostly remembered so many numbers thanks to pattern recognition. I'm old enough to have had a rotary phone in the basement growing that I used less than the various other keypad phones in the house. Whenever I was dialing (literally) a newly learned number on the rotary phone, I to think of what it looked like on touchpad first. Although very quickly I'd get to know the rotary pattern as well.
Of course, this is likely totally a regular memory device people would use. I've done no reading on this so, so if Socrates was wary of writing, was he also wary of pattern recognition or drawing as memory aids?
Back in Socrates time, masters of rhetoric used https://en.wikipedia.org/wiki/Method_of_loci to memorize long texts without reading or writing. Something was definitely lost as something was gained.