telephone vs hold the line

telephone is a noun but hold the line is not a noun.

Word	Noun	Adjective	Verb	Adverb
telephone	Yes	No	Yes	No
hold the line	No	No	Yes	No

telephone (noun)	hold the line (noun)
electronic equipment that converts sound into electrical signals that can be transmitted over distances and then converts received signals back into sounds
transmitting speech at a distance

telephone (verb)	hold the line (verb)
get or try to get into communication (with someone) by telephone	hold the phone line open
	hold the line on prices; keep the price of something constant