Additional calendar-related features and issues within Microsoft Teams for Education
After reviewing the iphone app logs, it seemed like there was a bad server response from the cloud services related to authentication when joining meetings with voice. I considered that the MS cloud services must be clustered, so I continued to log out and back in until a different server authenticated me, and my issue went away.
To confirm my suspicion, many of the teams users in my office began to have the same issues concurrently with me. I had them all perform the repetitive logoff/logon process until their issues went away.
Presumably, MS has now resolved the server issue.