Antonyms for the phrase "headed up" differ depending on the intended meaning of the phrase. If "headed up" is used to mean "in charge of" or "leading," antonyms could include "behind" or "following." In contrast, if "headed up" is used to mean "becoming agitated," antonyms may include "calm" or "composed." Similarly, if "headed up" is used to indicate a direction of movement, antonyms may include "down," "backward," or "retreating." Overall, the antonyms for "headed up" depend on the context and intended meaning of the phrase, and may vary widely.