To transition a phone number from a physical device (Common Area Phone/User usage) to a Call Queue (Service usage), you must follow a specific lifecycle:

1. Unassign: A number cannot be modified or reassigned while it is actively linked to a user or device. You must first remove the current association.
2. Change Usage Type: Microsoft distinguishes between "User" (Subscriber) numbers and "Service" numbers. Call Queues and Auto Attendants require Service numbers. You must convert the usage type in the Teams Admin Center or via PowerShell to make it compatible with a Resource Account.
3. Assign to Resource Account: Once converted, the number is assigned to the Resource Account associated with the Call Queue to route incoming calls.

Microsoft Official Documentation: "Manage phone numbers for your organization." This section details the distinction between User (Subscriber) numbers and Service numbers and the requirement to change types when moving numbers between these categories.

Microsoft Official Documentation: "Assign, change, or remove a phone number for a user." Explains the necessity of unassigning a number before it can be repurposed within the tenant.

Microsoft Official Documentation: "Manage resource accounts in Microsoft Teams." Outlines the process of linking service-level phone numbers to resource accounts for Call Queue functionality.

Microsoft Learn (MS-700 Path): Plan and Configure Teams Phone – Module: "Configure and manage voice numbers." (Specific sections on Service Numbers vs. User Numbers).