Bobbing up is a phrase that describes movement of an object or person in an upward and downward motion. Some antonyms for this phrase could include "still," "motionless," or "stationary." These words suggest no movement or lack of action, in contrast to the energetic movement implied by bobbing up. Other antonyms could include "sinking," "drooping," or "descending," which convey a downward motion or loss of momentum. These words provide a clear contrast to the upward energy and buoyancy suggested by the phrase bobbing up. Overall, antonyms for this phrase can help to convey different levels of movement, energy, and direction.