This is an interesting question. Because I can still remember very well that almost all my friends memorized all the phone numbers of all their friends.
I did that too.
But since the people around me keep changing their phone numbers, I don't memorize them anymore. That's since prepaid phone numbers were trending.

Strangely enough, I can still remember all the phone numbers from the 90s. This is now probably memory junk. 😄
Including the numbers from the 90s, I can remember exactly 26 phone numbers. Excluding the numbers from the 90s there would only be four numbers in my memory.
And this nowaday phone numbers in my brain are still existing since many years.