The FlexSMART X2 has a built in microphone that only works when connected via Bluetooth. If connected via Bluetooth, do not have an AUX cord plugged into the Line In port of the X2.
Because the microphone only works when connected via Bluetooth, if your device is paired to the X2 but only connected for media audio but not phone audio, the microphone will not work. Please go into your devices settings for Bluetooth connectivity. Under the paired device list, open the settings menu for the paired FlexSMART X2. Make sure your device indicates it is connected to the X2 for both phone and media audio.
Please make sure the X2 is close enough to you to pick up your voice and that the microphone port on the X2 is not blocked or covered by anything.
Try testing the X2 with a different Bluetooth enabled device.
Please contact customer service if the troubleshooting above does not solve the problem.