There are a couple ways to upload files to Teams. Once you upload a file, you can also share a link to it. That way, you don't have to upload multiple copies of the same file to share it in different places.
Share a file in a one-on-one or group chat
Select Choose file beneath the box where you type a message. This will upload a copy of your original file. You can also upload a file by going to the Files tab of a chat and select Share.
You'll have access to files from your computer, OneDrive for Business account, and any third-party cloud storage you or your admin have added to Teams.
Share a file with your team in a channel
Choose file beneath the box where you type your message in a channel, or go to the Files tab and select Upload.
To attach a file to a message, tap Choose file below the box where you type a message, then select the file from your device or cloud storage service.Learn how to add third party apps to your iOS device.
There are a few ways to share a file that's already been uploaded to Teams. To access all files you've recently opened and your OneDrive, tap More > Files.
To share within Teams, go to the file you want and tap More options > Share. From there, you can search by person or group name in the Chat tab. The Channel tab will show a list of teams and channels, tap the channel you want to share with.
Other share options are Copy link—this lets you share a link outside of Teams—and Send a copy, which will download a copy of the file to your phone that you can then choose how you want to share the file.
To attach a file to a channel conversation or a chat, tap Choose file below the compose box and then select the file from your device or cloud storage service.
Upload files in the desktop or web app, and view them on your mobile device any time after that.
To share a file that's already been uploaded to Teams, swipe up from the navigation bar at the bottom of the app, then tap Files. Find the file you want (choose from cloud storage or the list of recently opened files) and tap More options > Share. From there, you can search by person, keyword, or group name in the Chat tab, and keyword or channel name in the Channel tab.