When it comes to finding synonyms for the phrase "is untruthful," there are a variety of options to choose from. Some straightforward alternatives might include words such as dishonest, deceitful, and fraudulent. Other options might include phrases such as insincere, disingenuous, or duplicitous. Depending on the connotation or context of the situation, there may be even more creative synonyms to consider, such as untrustworthy, mendacious, treacherous, or even sneaky. Regardless of the specific wording used, the core concept remains the same - if someone is described as being untruthful, it means they are not being honest or genuine in their actions or words.