phone service vs public utility

phone service and public utility both are nouns.

Word	Noun	Adjective	Verb	Adverb
phone service	Yes	No	No	No
public utility	Yes	No	No	No

As nouns, public utility is a hypernym of phone service; that is, public utility is a word with a broader meaning than phone service:

phone service: a public utility that provides telephone service
public utility: a company that performs a public service; subject to government regulation

Other hypernyms of phone service include public-service corporation, public utility company, utility.

phone service (noun)	public utility (noun)
a public utility that provides telephone service	a company that performs a public service; subject to government regulation