There are several synonyms for the phrase "fall by." One alternative is "drop by," which suggests a sudden decrease or decline. Another similar phrase is "slip by," which implies a slight or subtle change. "Decrease by" is another synonym, indicating a reduction in a specific amount or percentage. "Diminish by" is similar but implies a more gradual reduction. Meanwhile, "slide by" suggests something slipping away or passing unnoticed. "Decline by," "reduce by," and "lower by" all refer to a decrease in value, level, or quality. Finally, "sink by" implies a downward motion and is often used in more dramatic contexts.