S9 would be currently better at least in terms of volte calls if you give the unofficial build a try.
There are increasingly customrom Samsung builds that integrate “open VoLTE” of sorts (phh/ims derivations). ronnz builds the soc family too and has one variant here. You could ask for a r8q build:
I’ve asked murena if they consider integrating them, even if partially llm-driven, let’s see.