The antonyms for the phrase "break smithereens" would be to preserve, protect, and safeguard. When we use the phrase break smithereens, it generally means to break something into small pieces or destroy it completely. However, to use the antonyms of these words, we would aim to keep something whole and undamaged. For instance, to preserve a valuable vase, we would keep it in a secure location and take great care when handling it. We might also protect electronics from damage by using a protective case or keeping them away from water risks. In essence, we can use antonyms of break smithereens to indicate the act of keeping things safe and intact.