The phrase "not showing" can be expressed using a variety of synonyms, depending on the context in which it's used. If someone is not displaying any emotion or reaction, they might be described as "unresponsive," "impassive," or "stoic." In a different context, if something is not visible or present, it could be said to be "missing," "absent," or "invisible." Similarly, if someone is failing to fulfill their duties or obligations, they may be labeled as "neglectful," "derelict," or "indifferent." In all of these situations, there are a multitude of words and phrases that could be used to convey the same idea as "not showing".