Traffic Shaping

Using traffic shaping in order to give priority to VoIP phones. We wish to give all other traffic medium priority.

1. In this example, is it necessary to list all policies in the Traffic Shaping Policy or is it only necessary to list the VoIP policy in the Traffic Shaping Policy?

2. It appears that we could put the VoIP phones in a Device Inventory / Custom Devices Group by MAC address or we could create a policy listing SIP as the service. Which of these choices would be preferred?