Additional features, settings, or issues not covered by specific Microsoft Teams categories
Hello,
In order to obtain a business phone number, you will need to purchase additional licenses besides your Office 365, unless you are on the E5/A5/G5 plan.
Sign into your admin center via https://admin.microsoft.com using your business user credential.
Then go to Billing > Purchase. Search for calling plan, and you want to purchase the Teams Phone with calling plan. You might see more than one option. Depending on if you are calling domestic or international, or zone, you can pick the one that works for you. Once you purchased it, you can assign this license to your user.
Once thhat's done, go to Teams' admin center https://admin.teams.microsoft.com
On the left, click on Voice > Phone number. From there, click on Add to obtain your phone number. Once your phone number is obtained, assign to your user.