The phrase "missing in action" is often used in military or war-related contexts to describe soldiers who cannot be accounted for. Other synonyms for this phrase include "unaccounted for," "lost in combat," "disappeared," "absent without leave," "MIA," and "vanished." These terms all imply that an individual or group has gone missing and their whereabouts are unknown. In non-military contexts, other phrases that could be used as synonyms are "gone missing," "lost," "unfound," and "not present." These terms are often used in situations where someone has gone missing or disappeared, whether accidentally or intentionally.