There are many synonyms for the phrase "become expert in". Some of these synonyms include master, perfect, excel, specialize in, hone, and adept. Each of these phrases conveys the idea of becoming extremely skilled or knowledgeable about a particular topic or discipline. For example, if someone wants to become an expert in a specific field like medicine, they might choose to specialize in a certain area such as cardiology or oncology. Or, if someone wants to become a master of a particular skill like cooking, they might choose to hone their skills through practice and experience. Whatever the chosen synonym, the end goal is always the same: to become highly skilled and knowledgeable in a chosen area of expertise.