phone book vs phonebook

phone book and phonebook both are nouns.

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

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

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

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

phone 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