telephone directory vs telephone book

telephone directory and telephone book both are nouns.

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

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

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

Other synonyms of telephone directory include phone book, phonebook.

telephone directory (noun)	telephone 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