Get Phone Number

Retrieve a specific phone number by ID.

Parameters:
phone_number_id (int): The ID of the phone number to retrieve.
request (Request): The FastAPI request object.
db (AsyncSession): The database session (injected).
organization_id (Optional[str]): The organization ID from the API key or request.

Returns:
PhoneNumber: The requested phone number.

Raises:
HTTPException:
- 400: If organization ID is missing
- 404: If phone number is not found or not accessible
- 500: If an unexpected error occurs during retrieval