If you select your normal onboard sound device (Digital Audio ...) you have the same problem? I just want to know if this is a problem with the headset and how PhonerLite uses it.
You have two headsets and on one it should ring and on the other you want to hear the voice-data? I see the other is the default device (bold).

I can't reproduce that problem here. I had 20 incoming calls and all played the ring tone. Are you using the latest version (2.80) of PhonerLite?

I uploaded a new beta version of PhonerLite. That does some addition debug output, so I can see if opening a sound device failed or the ringing wave file could not be loaded. So you can download the beta version and extract the files over the exiting ones. All settings will remain of course. If you have a missing ringing tone for an incoming call, please copy the content of the debug window into an e-mail to me. You can show/hide the debug window via the help menu.