hello Tarun,

these messages usually are CDP derived.

Another thought is that speed and duplex are physical properties that can be configured only on the physical interface gi0/1.

So a complain for duplex mismatch is a true issue only if it is seen in

sh int gi0/1.

Then the IP phone should be the first device out the port.

In this case you should change the cable or verify cabling it can be a cable issue

or access via web the ip phone page and check for collisions errors or other signs that is putting the link in half duplex.

Hope to help

Giuseppe