Before opening a trouble ticket for your phone system please try these steps:
Make sure :
Your equipment (Phone, modem and router) is properly connected.
Your internet cables are properly connected.
The power outlet is working properly.
Your internet is working and you have internet on your other devices like your computers.
Unplug your SIP Phone, wait for 60 seconds, and plug it back in
If none of these help please open a Trouble ticket: