When it comes to expressing one's thoughts and plans, there are several synonyms for the phrase "be thinking of/about doing something." These alternatives include "contemplating," which implies a deeper level of thought and consideration, "pondering," which suggests a more reflective and introspective approach, and "mulling over," which implies a persistent and ongoing consideration of a matter. Additionally, examples of other synonymous phrases include "considering," "meditating on," "weighing up," and "entertaining the idea of." Overall, there are many ways to express the act of considering or planning to do something, and selecting the right synonym depends on the context in which it is used.