Check your sound settings
If your device has a Ring/Silent switch, move the switch forwards – towards the device’s display – so that orange isn’t showing. If you're using an iPad, you can also swipe down from the top right-hand corner to view Control Centre and make sure that Silent Mode is off.
Open Settings > Do Not Disturb and make sure Do Not Disturb is turned off.
Clean your receivers and speakers
Remove all screen protectors, films or cases from your device. Check the opening of the speaker to see if it's blocked or dirty. On iPhone only, make sure the receiver is not blocked or dirty. If necessary, clean the speaker or receiver opening with a small, soft-bristled brush. Make sure the brush is clean and dry.
Check the sound on your device
Go to Settings > Sounds (or Settings > Sounds & Haptics), and drag the Ringer and Alerts slider back and forth a few times. If you can't hear any sound or if your speaker button on the Ringer and Alerts slider is dimmed, your speaker may need servicing. Contact Apple Support for iPhone, iPad or iPod touch.
Try making a call
If you hear sound, try making a call with your iPhone and turn on speakerphone. On iPad or iPod touch, make a FaceTime call. If you still can't hear anything, or hear static or crackling, then your network or reception could be the issue. Try to calling again later or from a different location.
FaceTime isn't available in all countries or regions.