DSL vs phone line

DSL and phone line both are nouns.

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

As nouns, phone line is a hypernym of DSL; that is, phone line is a word with a broader meaning than DSL:

DSL: a generic name for digital lines that are provided by telephone companies to their local subscribers and that carry data at high speeds
phone line: a telephone connection

Other hypernyms of DSL include line, subscriber line, telephone circuit, telephone line.

DSL (noun)	phone line (noun)
a generic name for digital lines that are provided by telephone companies to their local subscribers and that carry data at high speeds	a telephone connection