After changing my domain password, the Microsoft Teams app on my iPhone signed me out, and I was unable to sign back in. When I would enter my username & password, it would go to a white screen with a spinning circle for several minutes and eventually time out. After trying several things I finally wondered if some of my content/privacy restrictions might be causing the problem & sure enough that was the case.
When I disabled the web content filter it worked. To configure this setting on an iPhone with iOS 13.x, go to Settings > Screen Time > Content & Privacy Restrictions > Content Restrictions > Web Content and set it to "Unrestricted Access"