The phrase "did one part" refers to a certain action or task that an individual accomplished or fulfilled. When it comes to antonyms for this phrase, several options are available, depending on the context of the usage. For example, instead of "did one part," one could say "failed to do one part" to indicate that someone did not fulfill their responsibility. Alternatively, one could use "did every part" to indicate that someone went above and beyond their required duties. Other antonyms might include "underperformed," "abstained," or "ignored," depending on the specific situation.