In Teams you may see Contacts on your Calls tab that are "missing" their phone numbers or the phone number may be incorrect.  Teams retrieves this information differently than Skype. 

For any user that is missing their phone number or has it showing incorrectly need to edit the phone number manually at My UofI Info:https://www.hr.uillinois.edu/myinfo

Once there click on My Profile and log in with your University credentials then edit your Office Address and add the phone number.

This process can take up to 28 days to sync correctly for any given user for any data source for any incorrect information.

User information isn't updated in Microsoft Teams: https://learn.microsoft.com/en-us/microsoftteams/troubleshoot/teams-administration/user-information-not-updated