Antonyms for the phrase "fills to overflowing" include words that signify emptiness or a lack of abundance. These words may include "depletes," "empties," "evacuates," "exhausts," or "departs." If something is not filling to overflowing, it could be described as "sparse," "scant," "limited," or "meager." The opposite of overflowing could also be "contained," "restrained," or "controlled." When we use antonyms, we can create a clear contrast between two things and showcase the different characteristics and features of each. Through antonyms, we can enrich our vocabulary and express ourselves with greater precision and nuance.