The cost of mailing phone books here would be prohibitive, so the phone people generally hire "messengers" to "hand deliver them." Postal regulations prohibit anyone putting anything that isn't "mail" in a mailbox, and the people who deliver them aint' mailpersons. It's a sporadic job, so I guess lots of the people who run them around are probably the same crowd as the S.C.s at Xmas time(?) or something of the sort.
But my mailbox is about average for the neighborhood, and you certainly could squeeze an average phone book into it. It's not that people need the volume but a generous box size saves you from getting your magazines and such curled up too tight make 'em uncurl so you can read them.
Newspapers here are rolled up and stuck into little plastic baggies, in case it rains, and tossed on the lawn in sort of a drive-by process. If I don't get mine picked up before the sun cooks it for a couple of hours I sometimes have to use a steam iron to flatten it out enough to do the xword puzzle.