Hi cburrows12,
If the sound is both unexpectedly low and distorted at full volume, this may be an issue with the speaker on your iPhone. There is one at the bottom of the iPhone and the top in the part you'd put to your ear on a call.
We'd first recommend restarting the iPhone and test if the issue is resolved.
"How to restart your iPhone 6, 7, 8, or SE (2nd or 3rd generation)
- Press and hold the side button until the power-off slider appears.
- Drag the slider, then wait 30 seconds for your device to turn off. If your device is frozen or unresponsive, force restart your device.
- To turn your device back on, press and hold the side button until you see the Apple logo."
If the problem persists after that, go to Settings > Accessibility > Audio/Visual and adjust the Balance slider all the way to the left, then play audio. If it sound clear and loud, then move it to the right and test again.
If side or the other is distorted, this may indicate a hardware issue with the speaker. We'd recommend contacting Apple Support for assistance at that point.
Take care.