verify that QoS is enabled:

Enable QoS:

At this stage, all interfaces are by default untrusted. This means that any frame with a priority value will be remarked as CoS/IP Precedence/DSCP value = 0.

Trust CoS values of incoming frames. Useful for trunks:

Trust CoS values only if an attached Cisco ip phone exists (conditional trust):

At this stage, the trust boundary moves to the IP phone. Any priority value of any attached PC frames is untrused, thus remarked with priority 0.