telephone service vs phone company

telephone service and phone company both are nouns.

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

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

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

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

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