There are several synonyms for the phrase "took upon," including undertaking, assuming, accepting, shouldering, and tackling. Each of these synonyms suggests a sense of responsibility and action. Undertaking implies willingly agreeing to handle a task or responsibility, while assuming suggests taking on a responsibility that may not have been assigned to you. Accepting implies acknowledging and agreeing to take responsibility, while shouldering suggests carrying the weight of a responsibility. Tackling suggests a proactive approach to a problem or task. Each of these synonyms can be used interchangeably with "took upon" depending on the context.