Speaker icon on iPhone

Seems like a hardware error with your speaker

Try this

If you prefer, here are some more steps you can try on your own. After following these steps, you may still need to contact Apple Support to discuss service options.

1. Remove all screen protectors, films or cases from your device. 
2. Check the opening of the speaker to see if it's blocked or dirty. On iPhone only, make sure the receiver isn't blocked or dirty. 
3. If necessary, clean the speaker or receiver opening with a small, soft-bristled brush. Make sure the brush is clean and dry.
4. 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 to be serviced.
5. If you can 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 you hear static or crackling, then your network or reception could be the issue. Try calling again later or from a different location.

see this Link for further reference

If you hear no sound or distorted sound from your iPhone, iPad, or iPod touch speaker - Apple Support