No dial tone in home phone

Just connected to NBN on aTelstra (Technicolor TG797 n v3) modem, and I now find that the phone connected to the Green Port does not have a dial tone. I can make calls and receive calls, so the phone works, apart from the no dial tone.

Also do I need a Splitter between the Mode and the phone?

The phone I have is a DECT phone, so should I connect to the DECT set up. If so, how do I do that? 

Thanks for the help/

KS