directory vs phone book

directory and phone book both are nouns.

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

As nouns, phone book is a hyponym of directory; that is, phone book is a word with a more specific, narrower meaning than directory:

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

Other hyponyms of directory include phonebook, telephone book, telephone directory, blue book.

directory (noun)	phone book (noun)
an alphabetical list of names and addresses	a directory containing an alphabetical list of telephone subscribers and their telephone numbers
(computer science) a listing of the files stored in memory (usually on a hard disk)