My first thought is, that you maybe try a different DNS server, like cloudflare or quad9 or whatever you like. Or set it to 10.6.0.1 to get the DNS from your PI.
You can change this setting directly on your phone, if you use the android wireguard app then this is pretty straight forward.
I don’t think it’s a config issue, since you generated it with PiVPN and used also the QR code to bring it to your phone.
You can also have a look into the logs of the VPN app, if the handshake happens or if you find other hints.
The address you don’t know are coming from the newly created wg0 interface for the VPN. The interface itself has usually (With PiVPN at least) 10.6.0.1 and the “clients” the following IPs.