best response confirmed by ThereseSolimeno (Microsoft)
Solution

@fstorer 

 

I had this same issue today and after MUCH troubleshooting, here are the steps we took to rectify the issue:

 

1. Deleted the Teams app from iPhone. 
2. Followed link from invitation email (which opened browser)
3. Clicked Create New Account on login screen (which prompted login creation and verification codes).
4. Prompted to download app
5. Downloaded App
6. Signed in with new creds
7. Was able to see correct Org and Teams.
 
Also to clarify we did NOT have to do any of these steps on the computer ONLY on the mobile device. Seems like a bug to me.