phone company vs public utility

phone company and public utility both are nouns.

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

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

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

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

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