The antonyms for the phrase "did a service" include "failed," "neglected," "hindered," "obstructed," "opposed," "retarded," "hurt," "damaged," and "weakened." These antonyms suggest that the action of "doing a service" involves actively contributing to a positive outcome, while their opposites involve either inaction or actively working against the desired outcome. It is important to note that the antonyms for "did a service" are not necessarily negative in every context; for example, sometimes it is necessary to "oppose" certain actions or individuals in order to ultimately do a service for others.