My phone rings loud two times then goes real low?

I have the same issue, iPhone 11 rings loudly twice and then barely audible. I believe I have fixed it without turning off Face ID. Instead I changed a setting within Face ID by turning off the slider for "Attention Aware Features," which "lowers the volume of some alerts."

Do you have facial recognition set up? Does it go quiet when you look at the phone? That is normal. If you want to to remain loud, turn off facial recognition or don’t look at who is calling.

This fixes it without turning Face Recognition off.

https://youtu.be/ZR5zJFnicGY