It was more than just the phone books. Back before smart phones, if you needed to look up a phone number you’d call information (411) and they’d look it up for you. For instance, if you were stuck on the side of the road and needed a tow truck.
Information would be able to look up businesses close to where you were using the NPA/NXX of the phone number you were calling from (the first six digits of the number including the area code) and then give you a couple options in alphabetical order.
I had a client who had a phone number in every exchange in NYC and had a name like “AAA Towing” so no matter where in NYC you called information for a tow truck from, they’d usually be the first option given to you.
Can’t figure out if this is a joke or serious, so just in case, you might want to look up what happened to the Library of Alexandria.