The antonyms for the phrase "not up to scratch" are quite varied, and they can be used to convey different meanings depending on the context. Some of the antonyms that can be used to describe something that is of high quality and meets expectations are "excellent," "superior," "outstanding," or "exceptional." If you want to emphasize that something is of good quality, you can use words like "adequate," "satisfactory," "sufficient," or "acceptable." On the other hand, if you want to highlight that something is lacking or deficient, you can use terms like "substandard," "inferior," "unsatisfactory," or "below par.