The top speaker is very quiet

Try and force restart the iPhone to see if the issues persist

1. Press and quickly release the volume up button.
2. Press and quickly release the volume down button.
3. Press and hold the side button.
4. When the Apple logo appears, release the side button.

If that is not working try this:

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.

If the issue persists you'l need to contact Apple Support to discuss service options.