phone line vs telephone circuit

phone line and telephone circuit both are nouns.

Word	Noun	Adjective	Verb	Adverb
phone line	Yes	No	No	No
telephone circuit	Yes	No	No	No

As nouns, phone line and telephone circuit are synonyms defined as:

Other synonyms of phone line include line, subscriber line, telephone line.

phone line (noun)	telephone circuit (noun)
a telephone connection	a telephone connection