Classification and Marking of softphone applications
It is possible to do this from the application. For example, Skype or Webex can do this.
If you don't trust the applications, you can also do this using QoS Network Based Application Recognition (NBAR). Here is a quick example how do to classification of Skype traffic using NBAR and prioritize this traffic:
class-map SKYPE match protocol skype policy-map OUTBOUND class priority priority 5000 interface GigabitEthernet0/1 service-policy output OUTBOUND