Hello,
In the organization I manage, we have all employees' phone numbers entered in Admin Center for each user.
For example, if you go to Admin Center https://admin.microsoft.com Sign into your admin user.
On the left, click on Users > Active users. Select one of them for example, the user card will slide out from the right. Scroll down and click on "Manage contact information". Then for the Office Phone field, go ahead and enter the phone number. If extension is involved, it can be in this format: +1xxxxxxx;ext=xxx
Once you have that entered and saved, in Outlook or Teams, you can click on this user icon, in the Contact tab, the phone number will be shown. On the phone, you also click on user icon > view profile and the phone number will be shown too.
Could that be what you might be looking for?