The Ceres BT speaker does not have a microphone, nor do any of the inputs transmit audio to the Bluetooth connection. You can listen to your mobile phone’s audio output on the Ceres via Bluetooth but you still need to use your phone as the microphone.
Please note that if your phone is in front of your speakers while on a call, the volume of your speakers may cause a feedback loop if the microphone on your phone can pick up the speaker output. Be sure to keep your phone out of the direct path of the output of your Ceres speakers to avoid this problem.
Please contact PreSonus Technical Support by creating a Support Ticket at My.PreSonus.com for further assistance.