in small stages vs step-by-step

in small stages and step-by-step both are adjectives.

Word	Noun	Adjective	Verb	Adverb
in small stages	No	Yes	No	No
step-by-step	No	Yes	No	No

As adjectives, in small stages and step-by-step are synonyms defined as:

Other synonyms of in small stages include bit-by-bit, piecemeal, stepwise.

in small stages (adjective)	step-by-step (adjective)
one thing at a time	one thing at a time