The phrase "in the matter of" is often used as a legal term to indicate that a specific issue or case is being discussed. However, there are several other phrases that can be used as synonyms for this term, such as "with respect to", "concerning", "regarding", "in relation to", "pertaining to", and "on the subject of". These phrases can be used interchangeably with "in the matter of" in legal documents, contracts, and other professional communications. Using synonyms can add variety to your writing and make it easier to understand, while still conveying the same important message.