Adding M365 to Outlook on mobile device

To add your M365 account to a mobile device, install Outlook from the Google Play Store, or Apple App Store.

Open the app on your phone
(The following screenshots are from an Android device, but iPhone and iPad will be similar)

 Navigate to settings, my device already had one account in, so I had to click on my picture in top left and then on the cog in bottom:

Then click on "ADD EMAIL ACCOUNT":

At the bottom of screen click "Add an email account":
NOTE: You can come back here to add a shared mailbox later.

On my phone I already had my Sutton Scouts address from another application.
If this is the case with your phone, add a tick to all the accounts you wish to add, as per the screenshot below and click "Continue" , otherwise go to the bottom and click "skip these accounts":

Assuming you clicked skip these accounts, enter your email address in the box just under the graphic saying "Enter your email"
Then click "Continue" at the bottom:

My device tried to connect to Google, as can be seen below, click on "NOT GOOGLE" at the bottom if this happens to you:
(Notice the "Sign in with Google" towards the top.

Then click on "Changed account provider" at the bottom of this screen:

Select "Office 365":

Enter your password:

Your account is now added:

Each of your accounts is available by clicking on the icons in the top left: