I guess it's fewer than I thought. Aside from current phone numbers for our land line, cell, wife's cell, parents and brother, there's my grandparents' house, where my uncle now lives - that number has rung at that house continuously since 1959. Our old house phone growing up, and the old numbers for my friends John and Jim from high school, my girlfriend during college, my wife's when she was my girlfriend (still got the post-it on which she wrote it down)... couple old work numbers, my old boss who lives in the neighborhood, couple local restaurants where we get take out., and some from earworm jingles like Empire Carpets and Kars 4 Kids.
And some weird ones, like I realized I remember the number for the PBS TV station from Schenectady. Why on earth would I remember that? countless pledge drives, I guess... but I haven't watched that station in over 30 years. Why would that knowledge even occur to me? Brains are weird.
Clearly having a phone with numbers stored has eliminated the need to remember them... also probably eliminated an important form of brain exercise.