Antonyms for the phrase "were of use" can vary depending on the context. Some possible antonyms include "were ineffective," "were useless," "were detrimental," "were harmful," or "proved to be a hindrance." These antonyms suggest that instead of being helpful and beneficial, the thing or action in question had a negative impact or failed to serve its intended purpose. It is important to consider the specific context in which the phrase "were of use" is being used before determining suitable antonyms, as the opposite of usefulness can be subjective and may vary depending on the situation.