Call volume is very low on my iphone8 plus. Turning off noise cancellation did not help.

Hello ypshen0828,

Thanks for visiting Apple Support Communities. We understand that you're having an issue with the volume of your phone calls. Complete the steps in the following guide to see if they help: If you hear no sound or distorted sound from your iPhone, iPad, or iPod touch speaker

If the behavior continues, let us know more:

• Does this happen with all calls and in all areas?
• Does the behavior continue if you use headphones?

The more details you can provide the better.

Take care.

ypshen0828,

Thanks for letting us know the behavior continues. Do you use a case with your iPhone, and if so, does removing it help? If not, you'll want to have your iPhone further inspected. To start looking into available options, start here: iPhone Repair

Best regards.