Please try these steps
- Remove all screen protectors, films, or cases from your device.
- Check the speaker opening to see if it's blocked or dirty. On iPhone only, make sure that the receiver isn't blocked or dirty.
- If necessary, clean the speaker or receiver opening with a small, soft-bristled brush. Make sure that the brush is clean and dry.
- Go to Settings > Sounds (or Settings > Sounds & Haptics), and drag the Ringer and Alerts slider back and forth a few times. If you don't hear any sound, or if your speaker button on the Ringer and Alerts slider is dimmed, your speaker might need service.
- 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, or hear static or crackling, then your network or reception could be the issue. Try to call again later, or from a different location.
If this is not working, this is most likely a hardware issue. Please Contact - Official Apple Support
to set up hardware service for your device