The phrase "not the least" is used to emphasize that something is not even slightly important or relevant. Some synonyms for this phrase could include "not at all," "nevertheless," "by no means," "not one bit," "in no way," "not even remotely," and "absolutely not." These phrases can be used interchangeably with "not the least" to convey the same message. However, it's important to note that each phrase may have differing levels of intensity and tone, depending on the context in which they are used. Choosing the right synonym can help to convey the appropriate level of emphasis and meaning to the reader or listener.