The opposite or antonym for the phrase "loses strength" could be "gaining momentum" or "gaining strength." These terms imply a gradual increase in power, force, or effectiveness, which is the opposite of weakening. Another possible antonym could be "improving" or "recovering," which suggests a return to full functionality or potential. "Building up," "strengthening," "growing stronger," and "fortifying" are other antonyms that signify a positive progression in energetic or viable outcomes. Overall, the opposite of "loses strength" indicates a process of development and enhancement rather than a decline or deterioration.