There are many synonyms for the phrase "trained in," depending on the context in which it is used. Some possible options include "educated in," "skilled in," "versed in," "certified in," "proficient in," "experienced in," "instructed in," "versed in," "familiar with," "adept in," and "acquainted with." Each of these phrases conveys a slightly different shade of meaning, such as emphasizing the level of formal certification or education, the degree of practical experience, or the breadth of knowledge across a particular subject area. Choosing the right synonym can help to make your writing more precise and nuanced.