telephone book vs phonebook

telephone book and phonebook both are nouns.

Word	Noun	Adjective	Verb	Adverb
telephone book	Yes	No	No	No
phonebook	Yes	No	No	No

As nouns, telephone book and phonebook are synonyms defined as:

telephone book and phonebook: a directory containing an alphabetical list of telephone subscribers and their telephone numbers

Other synonyms of telephone book include phone book, telephone directory.

telephone book (noun)	phonebook (noun)
a directory containing an alphabetical list of telephone subscribers and their telephone numbers	a directory containing an alphabetical list of telephone subscribers and their telephone numbers