@yeshyeshyeshAccording to the modem specs it is not a PoE device. You would need to go out and purchase a 3rd party PoE switch that would connect into the modem as well as into the Polycom phone to allow it to function on PoE.
Agreed on if it is just the single device that a PoE injector would be the best bet (Unless you are expanding to additional devices later. Yay future planning).
One thing to make sure is to validate what version of PoE the device supports ( 802.3af (PoE) and 802.3at (PoE+)) as each one supports different wattages and make sure that the PoE device is sending out the right amount of power to the endpoint.