To configure the Vigor2830Vn for PSTN calls to ONLY ring on Phone1 you need to telnet to the router and run the command:

voip dsp pstnringfxs 

The syntax is:
voip dsp pstnringfxs [1|2] [on|off]
[1|2]:1.FXS1, 2.FXS2

example: Disable PSTN ring FXS2
> voip dsp pstnringfxs 2 off

To check the status run the command: “voip dsp pstnringfxs ?”
% ========PSTN ring FXS status========
PSTN ring FXS1 : enable
PSTN ring FXS2 : enable