When configuring 802.1X authentication on edge ports of an AOS-CX switch and assigning VoIP phones to a "voice" role, the correct approach is to configure VLAN 12 as the allowed trunk VLAN in the "voice" role. This setup ensures that traffic tagged for VLAN 12 is appropriately managed by the role applied to the VoIP phones. In AOS-CX switches, the role-based VLAN configuration allows for more granular control and ensures that the VoIP phones' traffic is handled correctly without altering the edge port settings, which typically operate with default settings for authentication.