Hello Aniket
Let me quote Rene from his lesson:
This is the image he uses:
Behind the scenes, we have a trunk between our switch and IP phone. The port on the IP phone that connects to the computer is an access port. The IP phone will forward all traffic from the computer to the switch untagged, traffic from the IP phone itself will be tagged. The only two VLANs that are allowed though, are the access and voice VLAN.
So, all traffic to and from the phone will be tagged (voice traffic) and all traffic to and from the PC will not be tagged (data). For more information about tags and how they work, take a look at this lesson:
I hope this has been helpful!
Laz