If changes or degradation in voice call quality after updating to iOS 12.1.1, you may need to change a Cellular Setting. This change will only need to be made if the following conditions are met:
Have updated iPhone to software version 12.1.1 or above
o Confirm under Settings > General > About > Version
Has or had Wi-Fi Calling enabled
o Confirm under Settings > Cellular > Wi-Fi Calling – If the user has it turned off, but has enabled the service previously, then flipping the toggle back on will display an “Enable Wi-Fi Calling? > Enable” pop-up with no further actions required.
Enable LTE menu is set to Voice & Data
o Confirm under Settings > Cellular > Cellular Data Options > Enable LTE > Voice & Data
If you do not meet any of these conditions, continue with normal troubleshooting.