The antonyms for the phrase "most ensured" can vary depending on the context in which the term is being used. However, some potential antonyms that might apply include "least assured," "uncertain," "risky," "insecure," and "unprotected." When used in the context of insurance or safety, for example, "most ensured" might refer to something that is highly protected or guaranteed, such as a secure investment or a safety measure that is certain to work. The opposite of this might be a situation or action that is uncertain or risky, such as an investment with no guarantees or a safety measure that is unreliable.