A simple comparison between the SIP traffic of your soft clients and the phone should help you to identify the issue.
Please ensure to provide some feedback on your old post if this reply has helped you so other users can profit from your experience.
Polycom Global Services
Notice: This community forum is not an official Poly support resource, thus responses from Poly employees, partners, and customers alike are best-effort in attempts to share learned knowledge. If you need immediate and/or official assistance please open a service ticket through your proper support channels. Please also ensure you always check the VoIP , Video Endpoint , Skype for Business , PSTN or RPM FAQ's