The phrase "come up again" can be replaced with a variety of synonyms depending on the context. In the case of a topic or issue being revisited, words like reappear, resurface, or recur can be used. When discussing an item returning to a previous location, words like return, come back, or revisit may be more appropriate. For situations where an idea or suggestion is brought up again, words like reintroduce, suggest anew, or propose again can be utilized. Whichever synonym is chosen, it should reflect the specific circumstances and context of the situation in which the phrase is being used.