on an individual basis vs one by one

on an individual basis and one by one both are adverbs.

Word	Noun	Adjective	Verb	Adverb
on an individual basis	No	No	No	Yes
one by one	No	No	No	Yes

As adverbs, on an individual basis and one by one are synonyms defined as:

Other synonyms of on an individual basis include individually, separately, severally, singly.

on an individual basis (adverb)	one by one (adverb)
apart from others	one piece at a time
	apart from others
	in succession