There are several synonyms for the phrase "churns up". One of these synonyms is "agitates", which means to disturb or upset the normal state of something. Another synonym is "roils", which refers to the turbulent or tumultuous movement of water. "Stirs up" is another synonym, which implies the disruption of something or someone, and can also refer to the act of creating a commotion or disturbance. Yet another synonym is "riles", which indicates being or becoming vexed or angry due to a particular situation or event. These synonyms help to convey the same meaning as "churns up" in varying degrees.