Cisco 7925G Deployment Manual page 66

Select the method to submit a certificate request by using a base-64-encoded PKCS file.
Paste the certificate data from the Cisco Unified Wireless IP Phone 7925G to the Certificate Authority signing server and
submit for signing.
When the certificate has been signed, download the CA certificate in DER encoded format (base 64 encoded not supported).
Ensure Client Authentication is listed in the Enhanced Key Usage section of the certificate details.
After selecting "Import Step", browse to the signed user certificate and select "Import" to complete the process.
Cisco Unified Wireless IP Phone 7925G Deployment Guide 66