To clean a receiver, you will need a proper tool, and we suggest a toothpick, for example. When cleaning the receiver, be careful, and do it slowly and gently. Remover all the dirt, because it can make a huge difference.
Sometimes, you can accidentally turn the volume down, so make sure to check that out. When talking to someone over the phone, simply press the volume buttons which are located on the side of the device.
Press and hold the sleep/wake button and drag the slider to turn off your phone. Press and hold the sleep/wake button to turn your iPhone 6 Plus back on.
If in some case, the Bluetooth is on, it may cause the problem. To turn it off, go to Settings > Bluetooth.
Before you do this, back up your files to iCloud. Go to Settings > General > Reset > Erase all Content and Settings. Leave the phone do the task, and when it is done, set up your iPhone 6 Plus as a new device, by simply following the simple steps.