UC Softphone Voice Quality

The first option is to log out of the Softphone app and shut down and restart the device, then log back into the app and test.

When Connected via WiFi 

Internet speed and latency may be a factor, please run a speed test here and share the results, http://cybertel.speedtestcustom.com/
 
The WiFi signal strength is another important factor. To check your WiFi signal strength, there is an app called WiFi Analyzer, available in the App Store and Google Play. It is free. Install it on the device and run it and test the signal strength in the area where your receptionist works.
 
https://play.google.com/store/apps/details?id=abdelrahman.wifianalyzerpro&hl=en_AU&gl=US
 
There is also a Microsoft app for Windows if she is using the Softphone on a PC.
 
https://apps.microsoft.com/store/detail/wifi-analyzer-and-scanner/9NBLGGH5QK8Q?hl=en-us&gl=us
 
Run the scan and screenshot and forward us the results.