You can use Plantronics headset or call control unit accessory functional buttons Answer, Reject, Hangup and Hold\Unhold to control call.
1. Download and install Plantronics Hub from Plantronics official web-site.
2. Open Settings - Main section.
3. Enable Plantronics headset integration checkbox:
4. Click Save button.
5. Test your Plantronics headset functional buttons by making a test call in softphone.