brush up vs call back

brush up and call back both are verbs.

Word	Noun	Adjective	Verb	Adverb
brush up	No	No	Yes	No
call back	No	No	Yes	No

As verbs, call back is a hypernym of brush up; that is, call back is a word with a broader meaning than brush up:

Other hypernyms of brush up include call up, recall, recollect, remember, retrieve, think.

brush up (verb)	call back (verb)
bring to a highly developed, finished, or refined state	recall knowledge from memory; have a recollection
refresh one's memory	summon to return
	return or repeat a telephone call
	cause to be returned