It wasn't the phone. It was Windows 7 being rediculously unpredictable. It doesn't even seem to care what settings we have. Even when we can get Windows 7 working... it often breaks TLS because the Skype for Business certificate is issued in the same exact common name and Windows 7 gets confused.
We actually gave-up on Windows 7 being smooth with this system and have started a push to get to Windows 10.