one by one vs on an individual basis

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

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

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

Other synonyms of one by one include individually, separately, severally, singly.

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