Conversations involving multiple participants, allowing collaboration and information sharing in Teams
Hello there, thanks for reaching out to Forums. I will be more than happy to assist you.
I understand that you're having problems with the MS teams chat on your mobile app but no issues with the desktop app and have already contacted Administrator. Base on my experience as MS teams Admin, I used to disable and re-enable chats permission and wait it to sync. In your end, once the Admin has done the mentioned steps, try to reinstall the app.
Hope this helps.