By default settings, every call is made from the GUI goes over Polycom phone, if the phone is on-hook position then call is diverted to speak phone.
You can set the connected headset to Polycom phone as default device so that that all incoming and outgoing calls use your headset. At any time you can switch to handset or speakerphone mode.
To set up headset as default device you must enable, and then activate, Headset Memory Mode.
TO ENABLE HEADSET MEMORY MODE:
1. Select Settings from Home view, and select Basic > Preferences > Headset > Headset Memory.
2. From the HeadsetMemoryMode screen, select Enabled.
3. To activate HeadsetMemoryMode, press headset button on the phone twice.
Now, whenever you answer a call, the call will connect to your headset automatically.