When it comes to antonyms for the phrase "am up to", there are several that come to mind. The phrase typically suggests that one is engaged in some sort of activity or endeavor, but an antonym might be "am not doing anything." Another possible opposite could be "am at a standstill" or "am stuck," indicating that one is unable to move forward with anything. Similarly, "am finished" or "am completed" might be a relevant antonym, indicating that whatever activity one was engaged in has come to an end. Overall, antonyms for "am up to" tend to connote a lack of action or progress.