This is a holder page for a bit more information on the issue but basically Phonon won’t retain it’s settings. The clearchat works fine but Phonon won’t use it by default or hold the priority you give it.
The short answer is to install pavucontrol
sudo apt-get install pavucontrol
Then run pavucontrol and turn your internal mic off and Phonon will then use your USB Clearchat. Enjoy