Hi Juliedh12,
Welcome to the Apple Community.
It may be that Voice isolation during phone calls will become available in future iOS.
Seems there is often a learning curve after software updates.
... you should still have Voice Isolation ok on your iPhone model.
Apple Support article "Models that support Spatial Audio, Voice Isolation, and Wide Spectrum"
The List includes:
"iPhone 11
iPhone 11 Pro
iPhone 11 Pro Max"
Complete article: https://support.apple.com/en-au/guide/iphone/aside/iph59938f591/15.0/ios/15.0
You can add voice isolation during FaceTime calls.
Another article: Change FaceTime audio settings on iPhone
Says:
"During a FaceTime call, open Control Center, tap Mic Mode, then select Voice Isolation"
Complete article: https://support.apple.com/en-au/guide/iphone/iphb54d5dee2/ios
Hope this helps you :-)