subscriber line vs phone line

subscriber line and phone line both are nouns.

Word	Noun	Adjective	Verb	Adverb
subscriber line	Yes	No	No	No
phone line	Yes	No	No	No

As nouns, subscriber line and phone line are synonyms defined as:

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

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