phone company vs phone service

phone company and phone service both are nouns.

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

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

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

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

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