The phrase "flip one's top" is primarily used to describe someone becoming angry or losing control of their emotions. There are several synonyms for this phrase that can be used to add variety and depth to your writing. Some possible options include "blow one's lid," "lose one's cool," "see red," "fly off the handle," and "go ballistic." Each of these phrases conveys a similar idea but may be more or less appropriate depending on the context in which they are used. By incorporating these synonyms into your writing, you can add dimension to your characters and create a more vivid and engaging story.