bit-by-bit vs in small stages

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

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

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

Other synonyms of bit-by-bit include piecemeal, step-by-step, stepwise.

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