The phrase "be the matter" is commonly used to refer to a problem or issue that needs attention. There are several synonyms that can be used in its place, including "be a concern", "be an issue", "be a problem", and "be at fault". These phrases all convey a sense of something being wrong or requiring action, and can be used in a variety of contexts. Other synonyms for "be the matter" include "be the problem", "be the cause", and "be the source of trouble", all of which imply that there is a specific reason for the issue that needs to be addressed. Whatever phrase is used, the message is clear - something needs to be done to resolve the problem.