Using an iPhone/iPad as a visualiser

Teams allows you to use your mobile device as a visualiser. Note that for the best experience you may need a suitable pile of books to balance your phone on, as pictured below. For a more professional and robust finish than 'a pile of books' you could use a goose neck smartphone holder / phone stand. There are many different ones available for £10-20 on Amazon and other online retailers.

If you would like to use an iPhone/iPad as a visualiser within Teams, then this can be done as follows:

Install Microsoft Teams on your iPhone/iPad from the Apple App Store
Log in as normal, ie specify your email address first and then sign in with your single sign-on account.
Join a meeting as you would normally do on your desktop/laptop - it works best if you use iPhone/iPad as a secondary device as your main device will still be streaming the video feed of you.
Once in a meeting, open Teams on the iPhone/iPad, you will see an "In progress: Meeting" on the top and can click "Join" to join it. Alternatively you could join from calendar or chat channel if that is how you did it initially.
Press on the three dots in the meeting toolbar and select "Share"
Click on "Share Video"
Ensure your device is displaying in landscape format
To start presenting your video press "Start presenting"
To stop sharing the video stream, press "Stop presenting"