Hello dfsfsdf dfsdfsdfsdf,
Most PCs and some other types of devices send traffic untagged only. Considering you can only have one VLAN that is untagged on a port the switch will automatically place this traffic in the untagged VLAN.
The phone will act as a switch and take the PC traffic and forward it as untagged and then send it's own traffic as tagged. In order to tell the switch this is happening usually there is a protocol like LLDP to communicate with the phone.
Here is an article that explains tagging a little better:
https://gtacknowledge.extremenetworks.com/articles/How_To/Understanding-EXOS-VLANS-and-tagged-and-un...
Hope this helps!