With a doublet jack was the PC and the phone simultaneously

Indeed, with Cisco, we must reverse the headphones and the microphone (and have the sound in one ear).
Otherwise ressertir the RJ9 jack by putting the right order:
spend Yellow Green Red Green Yellow Black Black to Red.
And have sound in both ears (tested Approved).
To get sound from your PC and the phone using the same headset without touching the connections all the time, use a jack splitter (1.5):
male: headphone jack adapter,
Female 1: headphone jack,
2 female: end of a cable jack M / M jack (the other end into the headphone socket of the PC to the cable, search)
Such is tested and approved by against it was the same sound in both ears in the headphones, not stereo.