There are several synonyms for the phrase "swallowing up," which means the act of engulfing or devouring something completely. One similar expression is "engulfing," which implies the same meaning of a large entity absorbing something smaller. Another similar phrase is "consuming," which has connotations of devouring and using up completely. The term "absorbing" can also be used to describe the process of taking in or assimilating something, while "devouring" suggests a sense of aggression and urgency in eating or absorbing something. Overall, these synonyms convey a similar sense of something being consumed or taken in completely, emphasizing the overpowering nature of the act.