The Phone Numbers Tab page is populated by phone numbers that are currently allocated to your org via Natterbox. This includes numbers that were ported or provisioned and whether they are allocated to an individual or are used org wide.
If you purchase additional numbers through Natterbox then you must come to this page and click on the
sync button to pull the numbers into the list and make them usable.
The Phone Numbers tab allows you to view available and unavailable numbers. Numbers can be used in routing policies and assigned as DDIs. If a number is being used in a routing policy it cannot be used in a DDI, this is because numbers assigned as a DDI, route using the DDI calls policy. The DDI calls policy can be customised to overflow to the wider team or leave a voicemail if the user is unavailable.
Assigning a Number as a DDI
Navigate to the Phone Numbers tab. To do this, click on the App Launcher in the top left-hand side of your Salesforce screen(9 dots) and search Phone Numbers

Click Edit next to the Phone Number which you want to assign to a user (as a DDI)

If the desired Phone Number isn’t in the list of numbers, press the Sync button next to where it says New Phone Number

Once the page loads, click on the Magnifying Glass next to where it says Natterbox User

Select the Natterbox User from the list, or search for the users name

6. Press Save

At this point, you will be sent back to the Phone Numbers tab, where you can check the Natterbox User is populated correctly with the user that you assigned the phone number to.

To remove the user just click edit again and remove the name of the user followed by save and now the number can be used in a policy again.
Video tutorial
Here is a video on how to add and assign phone numbers:
Reporting
If you need to report on your phone numbers and assignments all the above information can also be reported on using standard Salesforce functionality. The object is Phone Number (nbavs__PhoneNumber__c) and all the same fields are available and can then be exported and manipulated further outside of Salesforce (using excel etc..).
Please note: this data cannot be dataloaded back into Salesforce as it would not sync with the Natterbox platform.
To enable the Phone Numbers report type, following these steps:
Go to Setup > Object Manager
Find the Phone Numbers object
Click on the details tab, then ‘Edit’
Check the box ‘Allow Reports’
Save
For more info on reporting with the Phone Numbers object, see here.
sync button to pull the numbers into the list and make them usable.