welcome to the Polycom Community.
It is always useful to include the currently used UC Software version as issues experienced or a question asked may already be addressed in a newer release.
Please also include if you are using a SIP server or a LYNC / Skype for Business server.
This also allows yourself and others to check against current software release notes, Administrator Guides or FAQ post’s.
The above is also stated in the "Must Read First"
Therefore the Polycom VoIP FAQ contains this post here:
Question: How can I find out my SIP or UC Software Version of my Phone?
Resolution: Please check here
In addition when you state the caller cannot hear the ring? Is this the person using the Phone cannot hear a dial progress tone ?
Please provide more details with the above minimal requirement.
Please ensure to provide some feedback if this reply has helped you so other users can profit from your experience.
Polycom Global Services