Phone calls - answers ok but then call fails (so caller can’t hear me )

[Charles+pasfield]

iPhone 12 mini / iOS version 16.1.1

when someone calls this phone it can be answered but then after 2 seconds on frequent occasions the call just 'drops out'. It's like the other person can't hear. 
we've checked that Wi-Fi calling is enabled  and this happens when in the house so 4g good and Wi-Fi good. 
we've checked the obvious like phone on mute etc etc. 

really frustrating when trying to take an important call like from doctors or an ill relative. 

[Charles+pasfield]

...I just noticed my wife's phone not on the latest iOS version - so I guess that we should upgrade asap first? 

[caesarome]

There is no harm in updating it.