There are several synonyms for the phrase "by choice," including deliberately, willingly, intentionally, purposefully, and voluntarily. Each of these synonyms implies that the action was done with a sense of intention or will, rather than by accident or coercion. For example, someone might say, "I left my job by choice" to indicate that they made the decision to quit on their own accord. Similarly, if someone says, "I eat a vegan diet by choice," they are indicating that they have chosen to adopt this lifestyle rather than being forced to do so. Using synonyms can add variety to your writing and help you to convey your meaning more precisely.