Hello Dionisis
Yes you are correct in your description. Any traffic coming from the PC through the phone will be untagged and will go to the access VLAN configured on the port of the switch. All voice traffic is tagged and will go to the voice vlan configured on the port of the switch.
Keep in mind that the voice vlan configuration not only configures the appropriate VLANs for data and voice, but also sends voice traffic with a QoS based on IEEE 802.1p CoS. In other words, a Quality of Service technique is automatically incorporated into the functionality of the voice VLAN.
I hope this has been helpful!
Laz