The synonym for the phrase "most second banana" can vary depending on the context it is used in. However, some possible alternatives could include "second in command," "assistant," "deputy," or "right-hand man/woman." These terms all suggest a person in a subordinate role or position of support to a more prominent figure. Additionally, other related phrases could include "sidekick," "wingman," or "companion," which also imply a supportive or assisting role. Ultimately, the most appropriate synonym will depend on the specific context and the relationship between the two individuals involved.