Teams Resource Numbers are for Teams Call Queue's and Auto Attendants.
How does it work?
When a customer is enabled for Teams, under the customer menu in Connect you can click on Microsoft Teams/Resource Numbers. From here you'll see all the customers Call Queue's and/or Auto Attendants. The main purpose of this is to view and route these numbers. The "update from Microsoft / Re-Sync button will pull info from O365 and grab the appropriate name/phone number as long as it's listed as available and then automatically add the routing. Now you can visually see the name/number of the customers Queue's/AA's.
If a phone number was already set as unavailable manually and you hit update then you'll see unavailable under Display Name. This means you should verify that number isn't being used for anything else and then mark it as available. Then press the update button again and then it will go ahead and mark that DID as unavailable as well as update the routing.
If you notice the message Unrecognized DID under Display Name then that means that phone number either doesn't exist at all in Connect and/or for that company. Once you resolve that issue by either choosing the correct phone number in O365 and/or adding the number in Connect then press the sync button again to fix Display Name as well as routing.