The phrase "not that I'm aware of" is used to indicate uncertainty or lack of knowledge about a particular topic. However, there are many other phrases that can be used to convey a similar meaning. For example, "to the best of my knowledge," "as far as I know," "to my understanding," "I have no information to the contrary," and "I'm not familiar with that." Each of these phrases can be used in different contexts to imply a lack of information or knowledge, without making definitive statements. Other synonyms for this phrase may depend on the context, the speaker's tone, and the level of formality required in a conversation.