Hi Priesley21,
Thanks for coming to Apple Support Communities for help today with FaceTime Audio.
Please see this page: If you can't make a FaceTime call on your iPhone, iPad, or iPod touch.
Please note: "FaceTime and FaceTime audio calling might not be available for all countries, regions, or carriers."
If the articles don't help, have you tested your iPhone mics? Do they all work? If the microphones on your iPhone aren't working.
Have you tested on Wi-Fi?
Have a fantastic day!