Level off is a phrasal verb that could mean to stabilize or reach a plateau. Its antonyms, on the other hand, are words that have an opposite meaning to the phrase. One antonym for level off is to increase, which means to get larger or grow in size or amount. Another opposite word is to decrease, which means to lessen or become smaller. The third antonym for level off is to fluctuate, which means to change in an irregular way, going up and down frequently. Finally, the fourth antonym for level off is to decline, which means to decrease gradually in strength or quality. Therefore, the antonyms for level off are increase, decrease, fluctuate, and decline.