The phrase "flocks together" can be substituted in several ways based on the context. In social settings, you might use the phrase "birds of a feather" to indicate that similar personalities or interests tend to group together. In business, "networking" might be used to describe the practice of forming professional relationships. "Crowds" is another synonym that can be used when referring to large groups of people gathering for an event or activity. On a more negative note, "cliques" or "exclusive groups" can be used to describe a group of people who exclude others and don't allow new members to join. In summary, there are several words or phrases that can be used instead of "flocks together," depending on the context and intended meaning.