The phrase "am on the up" means to be improving or making progress. Antonyms for this phrase could include "declining," "regressing," "going downhill," "losing ground," or "worsening." These words suggest a negative shift or a decrease in progress or success. Alternatively, one could use phrases like "stagnating," "plateauing," or "reaching a plateau" to suggest a lack of improvement or progress. Additionally, words like "stuck," "stifled," or "held back" may suggest a lack of opportunities or resources necessary for growth and improvement. By using antonyms for "am on the up," one can highlight a lack of progress or a decline in a particular area.