There are several synonyms for the phrase "is liable" that can be used interchangeably in different situations depending on the context. Some of the most commonly used synonyms include prone, susceptible, accountable, answerable, and responsible. Prone and susceptible refer to the likelihood of something happening due to a specific circumstance or condition, whereas accountable and answerable refer to being held responsible for something. Responsible, on the other hand, denotes a sense of duty or obligation. Other synonyms that can be used include inclined, exposed, and subject to, among others. Using these synonyms in place of "is liable" can add variety and depth to your writing.