"Jumping in with both feet" is a figure of speech that means to immerse oneself in a situation without hesitation. There are several phrases that can be used as a synonym for this phrase. One alternative phrase is to "dive right in," which also implies that the person is ready to take on a task or challenge with enthusiasm. Another similar phrase is to "hit the ground running," which gives the sense that the person is starting out strong and eager. "Throw oneself into" is yet another synonym that conveys the idea of acting with energy and committement. Lastly, "take the plunge" is another common phrase used in place of "jump in with both feet," meaning to commit to something wholeheartedly.