What is another word for become less?
Pronunciation: [bɪkˌʌm lˈɛs] (IPA) 
There are several synonyms for the phrase "become less," including decrease, diminish, dwindle, wane, subside, abate, lessen, reduce, fade, ebb, lose intensity and recede. These words all convey a sense of something decreasing in quantity, intensity or strength. For instance, the intensity of a storm may decrease as it passes over an area. The amount of time someone spends on their phone may dwindle, or lessen, when they are busy with other tasks. The use of synonyms can help to vary your writing and avoid repetition, while still conveying the same meaning.
