Hi there
Welcome to the community,
Could you please send me a PM (private message) with your CID (customer identication number) or your mobile phone number so can look at this service for you 
Kind regards
HI there dortecooley0363,
Welcome to the community,
You actually do not need to plug your router into the phone line for your type of NBN service.
Your internet and phone service requires your TPG supplied (white) modem to be connected via ethernet cable to the (black) NBN arris box which then connects to the NBN coaxial wall socket.
Your phone sevice is now gererated from the TPG supplied (white) modem via the 2x grey telephony ports located on the back right side and this is where you must now connect your phone/cable. Be sure to use Phone port 1 when you plug it in.
You do have the right and option to relocate the current NBN coaxial socket and or to utilize the existing telephony cable in your premises however any costs you incur would be soley the responsability of yourself as a customer and not TPG your provider. Any Electrical or Telecommunications contractors must legally hold a current ACMA licence with the relevant associated endorsement requied ..
I would assume the now location of your phone itself at the back of the modem may be your issue and quite a common and inexpensive fix and alternative to cabling for customers is to purchase a cordless/wireless phone with addtional handsets.
While the main handset will need to plug into the phone port in the modem your addtional hansets can be put and work anywhere in your house and only need to plug into the power sockets.
I hope that has been helpful for you, if i can can help in any other way or if you have any further questions or concerns please let me know
Kind regards
Ken