phonebook vs phone book

phonebook and phone book both are nouns.

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

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

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

Other synonyms of phonebook include telephone book, telephone directory.

phonebook (noun)	phone book (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