Sadly, the only option is to turn wifi calling off. there is a script which says "When W-Fi calling is on, your phone can route calls via Wi-Fi networks or your carrier's network, depending on your preference and which signal is stronger." However, I am not consulted as to my preference.
Having done a little research, it appears that it is sometimes possible to toggle between Wifi and mobile preferred settings, but I've not found anyone who says you can do it on this particualr 'phone. Is it likely to be something model-specific?
