phone service vs phone company

phone service and phone company both are nouns.

Word	Noun	Adjective	Verb	Adverb
phone service	Yes	No	No	No
phone company	Yes	No	No	No

As nouns, phone service and phone company are synonyms defined as:

phone service and phone company: a public utility that provides telephone service

Other synonyms of phone service include telco, telephone company, telephone service.

phone service (noun)	phone company (noun)
a public utility that provides telephone service	a public utility that provides telephone service