static with hearing aids iphone 13

I have phonak hearing aids and have upgrade to iphone 13 and currently on ios 15.6.1

i have serious issues with static on a phone call when connected to the hearing aids (not with bluetooth in the car). This is a known issue and I have tried changing the phonak app to Adaptic Bandwidth and also the bluetooth connection of the hearing aid to Headphones, but the problem still exists. Phonak have told me to just change the app to Adaptic Bandwidth but its driving me crazy as I am on the phone for business alot and the call on the other end is telling me its a terrible line and they can't hear me propertly. Please help!

Interestingly there is a software upgrade to IOS 16 available, not sure if I should do this?