How does a Cisco IP phone handle untagged traffic that it receives from an attached PC?

A Cisco IP phone has an integrated switch that forwards untagged traffic from an attached PC directly to the upstream switch port without modifying its VLAN tagging state.

The IP phone is designed to facilitate PC connectivity, so it does not drop traffic from an attached PC unless due to a specific security policy or error condition.

The IP phone does not tag untagged PC traffic with a 'default VLAN'; it simply passes it through, and the upstream switch then assigns it to the appropriate data VLAN.

The IP phone passes untagged frames as untagged frames; it does not tag untagged PC traffic with the native VLAN, which is a concept primarily for trunk ports.