Look out for dust and lint gathering in the headphone jack if you have an older iPhone. Use a soft toothbrush and gently rub the speaker openings to loosen the dust. Keeping the microphone and speaker free of dirt makes interactions with Siri a lot easier. The SIM pin that comes with your iPhone is a really handy tool to clean the charging port. If you use a case, clean the phone at least once a week.

Source: The Telegraph January 06, 2019 11:48 UTC