You could also setup PiVPN[1] on the same Raspberry Pi running Pi-hole with Wireguard and setup all your mobile devices to automatically connect back home when they're off the home wifi.I've had this setup running for a couple of months now and couldn't be happier with it.
The WireGuard apps for iOS and OSX have a configuration section titled “On-demand activation” that lets you do this. On the iOS app, I have it set to activate on cellular connection and WiFi connections to routers if the SSID != my home router’s SSID. Likewise on OSX, except for the cellular option.
[1]: https://github.com/pivpn/pivpn