The phrase "put on ice" generally means to postpone or delay a particular action or decision. Antonyms of this phrase would include terms that signify taking immediate action or making prompt decisions. To this end, words such as "act now," "proceed," "urgency," and "immediacy" can serve as antonyms for the term. Other possible antonyms could include "accelerate," "speed up," "hurry," and "push forward," among others. These terms convey a sense of urgency and the need for immediate action, in contrast to the notion of delaying or deferring a task or decision.