"Catch up" is a versatile phrase that can be used to indicate everything from socializing with friends, to meeting deadlines, to coming up to speed on new developments. When trying to convey the same meaning in alternate ways, some synonyms that could be used include "get up to speed," "synchronize," "keep up," "fall in with," "align," "come up to date," and "keep pace." By utilizing synonyms, writers and speakers can emphasize different aspects of the concept of catching up depending on the context of their communication.