Hi Jeff_Sanders,
We see you've referenced the best article for fixing issues with the receiver on your iPhone, If you hear no sound or distorted sound from your iPhone, iPad, or iPod touch speaker.
The most helpful steps for the iPhone receiver are in section "If you want to try more steps on your own". Did you complete the following?
1. Remove all screen protectors, films, or cases from your device.
2. 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.
3. If necessary, clean the speaker or receiver opening with a small, soft-bristled brush. Make sure that the brush is clean and dry.
If so, the next step would be to reach out to Apple directly. This link will guide you there: Get Support
Take care.