A person who never uses Facebook for social networking but rather to accumulate an alphabetical list of people like a phonebook. A Facebooker that uses Facebook soley to respond to friend requests, but never posts a single status update, makes comments or even has a profile picture.
"Jane is such a phonebooker! She has 333 friends on Facebook and has never posted anything on her profile, not even a picture."
"Don't be such a phonebooker! Update your status every once in awhile!"