The phrase "turn inside-out" implies an action of reversing or flipping the orientation of an object or material, revealing its hidden side or underside. Some antonyms for this phrase could be "keep intact", "maintain original form", "preserve exterior", "leave unchanged", "keep outside-in", or "retain surface orientation". These antonyms suggest that there is no need to alter the current state of an object or material, and that its exterior or surface is sufficient for its intended purpose. In contrast, "turn inside-out" suggests a process of exploration, transformation or discovery. Ultimately, the antonyms for this phrase invite us to value the beauty and functionality of things as they are, without necessarily seeking to uncover their hidden sides.