Turn off ringer or disable calls?

Put the App on a tablet because we are constantly taking and texting photos to customers. Don’t want it to ring, because we have no need to answer a call on the tablet when we are surrounded by other phones.

I see nowhere in the app to turn off the ringer, or even adjust the volume. The tablet volume can be set to zero and it will still audibly announce a phone call.

Any way to either disable the ringer on the app, or force it to ignore phone calls and just allow texts?

Thanks. - Brett