Welcome to TPG Community!
We found a User Guide that may help you on how to configure your modem/router.
If you are going to use it as the main modem/router for your NBN FTTN service, you need to make sure that it will be configured with VLAN ID 2 and the connection type is PPPoE that will require your TPG username and password.
You may contact Netcomm support for further guidance with their modem.
The VoIP phone will not work on any Third party device.