caller-up vs speaker

caller-up and speaker both are nouns.

Word	Noun	Adjective	Verb	Adverb
caller-up	Yes	No	No	No
speaker	Yes	No	No	No

As nouns, speaker is a hypernym of caller-up; that is, speaker is a word with a broader meaning than caller-up:

caller-up: the person initiating a telephone call
speaker: someone who expresses in language; someone who talks (especially someone who delivers a public speech or someone especially garrulous)

Other hypernyms of caller-up include talker, utterer, verbaliser, verbalizer.

caller-up (noun)	speaker (noun)
the person initiating a telephone call	electro-acoustic transducer that converts electrical signals into sounds loud enough to be heard at a distance
	someone who expresses in language; someone who talks (especially someone who delivers a public speech or someone especially garrulous)