Antonyms for the phrase "reduce to ashes" can include words such as "build up," "preserve," "protect," "restore," and "save." These words denote actions that aim to strengthen, conserve, or improve rather than destroy. For instance, when we build up something, we add and enhance its components to make it stronger, more durable, or more efficient. Similarly, when we preserve, protect, or restore something, we work to maintain its original quality, prevent harm, or bring it back to its original state. Thus, while "reduce to ashes" represents destruction and loss, antonyms such as "build up" and "preserve" imply constructive and positive efforts.