The phrase "be past" can be replaced with a few different synonyms, depending on the context. One common synonym is "be over," which indicates that a particular timeframe or event has concluded. Another option is "be gone," which suggests that the time or opportunity has passed and cannot be retrieved. Additionally, "be finished" or "be done" can be used to convey that a particular task or project has been completed. Finally, "be behind" can be used to suggest that something has occurred and is now in the past, but may still have ongoing effects or ramifications. Overall, these synonyms offer flexibility in communicating the idea that something is no longer current or relevant.