The port roles are based on the type of devices to be connected to the switch ports.

IP Phone + Desktop: Apply this role to ports that are connected to IP phones.

A desktop device, such as a PC, can be connected to the IP phone. Both the IP phone and connected PC have access to the network and the Internet through the switch port. This role prioritizes voice traffic over data traffic to ensure clear voice reception on the IP phones.

Refer the URL: Catalyst Express 500 Series Switches Configuration:

http://www.cisco.com/en/US/products/ps6545/products_configuration_example09186a00806da6c9.shtml