From the service manual
Produces sound when connected to optional powered stereo speakers, headphones, earbuds, a headset, or television audio WARNING! To reduce the risk of personal injury, adjust the volume before putting on headphones, earbuds, or a headset. For additional safety information, refer to the Regulatory, Safety and Environmental Notices. NOTE: When a device is connected to the jack, the computer speakers are disabled.
This means the socket is faulty as it is supposed to cutout the speakers by a mechanism inside the socket itself. (My daughters phone as the opposite problem - no sound at all unless headphone plugged in.)
to replace the socket means wiring stripping the laptop and soldering on a new socket.