Regarding the Phoenix audio devices, some of these (as part of their own built in echo canceler) will suppress or turn off the microphone in situations where playback volume is too high or it detects that it may have problems cancelling the echo in the current environment. I would recommend downloading the Phoenix Audio Setup Utility and Audio Testing Wizard to see if this feature can be disabled. The Audio testing Wizard also allows you to create a sample recording and submit it to the Phoenix Audio support staff for evaluation.

You may find these utilities available for download here: http://phnxaudio.com/Support/tabid/69/Default.aspx