Only shared calendars that were accepted recently from Outlook on the web, iOS, Android or from Windows 10 Calendar will show up in mobile. If you have a calendar that you’d like to see in mobile, you can search for the calendar and add it directly in the app by using the + button in the menu from the Calendar view. Alternatively, you can ask the calendar owner to re-share the calendar to you. When you receive the sharing invitation in your inbox, accept the invitation from Outlook on the web, iOS, Android or from Windows 10 Calendar.
Note that the calendar owner can share the calendar from any Outlook app, but it’s easiest to do currently in Outlook on the web, iOS, or Android.
