When it comes to antonyms for the phrase "trumping up," there are a few options to consider. One possibility is to use the word "deflate," which suggests the opposite of inflating something - ie. making it seem less important or serious than it actually is. Another option might be to use the word "downplay," which suggests minimizing or making less significant. Alternatively, one could use the phrase "speaking the truth," which conveys the idea that there is no need to exaggerate or fabricate information. These antonyms all provide alternatives to the idea of "trumping up" something, which typically involves manipulating facts in order to make them more sensational or impactful.