The phrase "falls in with" means to agree or comply with something, and it is commonly used in speech and writing. There are several synonyms for the phrase "falls in with." If you are looking for a similar phrase with the same meaning, you may consider using "goes along with," "conforms to," "complies with," or "accedes to." Alternatively, you may also use "adjusts to," "adapts to," "assimilates to," or "fits in with." This can make your writing more diverse, interesting and provide more variety than using the same phrase repeatedly.