The phrase 'ebb down' means to decrease or diminish gradually. Antonyms for this phrase include build up, increase, rise, escalate, surge, expand, grow, and amplify. When something is building up, it is increasing in intensity or strength, while the opposite of ebb down is rise or escalate, which means to move or climb higher. Similarly, when something is surging or expanding, it is growing rapidly, which is the opposite of diminishing or ebbing down. Amplify is another antonym for ebb down, as it means to increase the volume or power of something. By using these antonyms, one can express a sense of growth, strength, or intensification, rather than decline or weakening.