PIA has a feature where the iOS app, and presumably its other apps, detect whether you’re connected using a cellular network or any number of known or unknown/public WiFi networks …. And you can set the app to take specific automated actions when it detects a change in network connection:
-always maintain current VPN connection status
-always connect to VPN
-always disconnect from VPN
etc.

Used in conjunction with the kill switch, you could… set your phone to disconnect from the vpn upon detecting connection through your home network but always enable the on-device vpn client when it detects you’ve switched to a cellular network or any other unknown Wifi…. And et voilà! Seamless, no leaks VPN connection. Just set it, and forget it!