Alfie wants you to try to connect to your wireguard server from outside your vodafone station.

You need to find your public IP address and connect to that with your wireguard client. Don’t try to connect to the AR750s IP inside the same lan.

Find your IP here: https://www.whatsmyip.org/

Put that in your phone wireguard configuration as the Endpoint address and try.

It is possible that you will not be able to connect in that way if Vodafone does not supply a public IP for you. That is not a GL router issue, it’s just how 4G carriers work, so please try that.