Antonyms for the phrase "making short work of" would be to struggle with, take a long time with, or labor intensely over a task. These phrases suggest that the task at hand is difficult or complex, and may require significant effort to complete. Similarly, phrases like "having a hard time with" or "taking forever to" also serve as antonyms to "making short work of." Ultimately, these antonyms suggest a slower, more challenging approach to completing tasks or achieving goals, rather than the quick and efficient approach implied by "making short work of.