The phrase "writing arm" often refers to the arm a person uses to write with, but there are other phrases that can be used to describe this body part. Some synonyms for "writing arm" could include dominant arm, favored arm, leading arm, or primary hand. Additionally, if the context requires a more specific description of the arm's function, such as for drawing or calligraphy, phrases like "artistic arm" or "creative arm" could be used. It's important to note that the use of these phrases may vary depending on the situation and preference of the speaker or writer.