There are several different synonyms for the phrase "is a member of." One common option is "belongs to," which implies a sense of ownership or association. Another possibility is "is part of," which suggests that the item or person in question is a crucial component of a larger whole. Additionally, "joins" or "participates in" can both be used to describe a person joining a group or organization. Finally, "enrolls in" or "registers with" may be used when discussing membership in academic or professional organizations. Overall, there are several different ways to convey the concept of belonging or membership, depending on the specific context and usage.