The phrase "is requisite" can be replaced with a variety of synonyms, depending on the context of the sentence. For example, the phrase can be replaced with "is necessary" when referring to something that is required or mandatory. Alternatively, "is essential" can be used to emphasize the importance of something, especially in situations where failure to meet certain requirements could result in dire consequences. Other synonyms for "is requisite" include "is compulsory," "is obligatory," "is crucial," and "is vital." In any case, it is important to choose the right synonym based on the intended meaning of the sentence and the tone of the writing.