The phone will not ring a second time for you.
Prior to The Trials of Gnomus update the path leading to the Chamber of Gnomes was sealed, and the message that you get about the second phone call dates from before this DLC launch.
One of the things that they did during the Trials update was open the pathway to the Chamber of Gnomes for everyone by default; which completely eliminates the need for the second phone call which used to provide you with the means to open it.
Unfortunately they seem to have forgotten to change the message referring to the second call which will no longer happen- which has lead to confusion for a lot of new players.