Hi, thank you for contacting JustAnswer.com. My name is Russell. I will do my best to provide the right answer to your question.
Does it at least announce incoming calls by vibrating?
If so - depending somewhat on what type of phone it is, cheap or expensive...
1. it may unfortunately have lost the power to produce sound! (double-check me on this one, if it actually still does produce sound demonstrably...) in which case vibrate 'ringing' may be a fallback for that sort of case, in the phone's workings.
2. volume might be very low.
3. volume might be Mute.
4. Make sure 'blocking' is Off.
5. Try pressing and holding the # *****
And there might be other things done for the problem, but check on those first, and let me know what model your phone is. Thanks.