It is possible for a Bluetooth speaker to have a built-in microphone, but this is not always the case. Some Bluetooth speakers are designed only for playback and do not have a microphone. If you are interested in purchasing a Bluetooth speaker with a built-in microphone, you should check the product specifications or the manufacturer's website to confirm that the device has this feature. Alternatively, you could also look for customer reviews or ask a salesperson for more information.