An antonym for the phrase "am on one's case" could be "am indifferent." This means that you are not paying attention or giving any importance to the issue or person in question. Another antonym could be "am supportive," indicating that you are helping and encouraging someone, rather than criticizing or constantly reminding them of their faults. "Am understanding" could also be an antonym as it represents showing empathy and compassion towards someone, rather than always being critical of their actions. These antonyms show different attitudes that one could have towards a situation or person instead of being on their case.