No, Switchvox and Digium Phones are not affected by the so-called "heartbleed" issue. Those products are not running the openSSL versions that are affected.
If you are using Polycom phone models that are supported and configured with a Switchvox Phone Feature Pack, the Polycom firmware that Switchvox installs is not affected. Polycom lists the firmware and phone-model combination as not vulnerable. (The same phone models are listed as vulnerable, if they are running different firmware versions than Switchvox includes). The Polycom security advisory is located here: http://www.polycom.com/content/dam/polycom/common/documents/brochures/heartbleed-security-advisory-enus.pdf
Symantec has a Certificate checker that you can run on any URL to test if it is vulnerable to the exploit: https://ssltools.websecurity.symantec.com/checker/