The phrase "do a service" can be replaced with various synonyms to add variety and clarity to communication. Some common synonyms include performing a duty, providing assistance, lending a hand, offering aid, doing a favor, extending help, rendering a benefit, delivering a task, and fulfilling an obligation. Each of these synonyms conveys a slightly different meaning and can be used based on the context of the sentence. Using these synonyms can help avoid repetition and enhance the overall impact of the communication. Furthermore, these phrases can help add a professional and courteous tone to one's language.