How do I open anothers person calendar on iOS with native calendar or Outlook App?

Hi Robert,

We don't offer an easy way to "open" another user's calendar in the Outlook mobile apps. (Nor does iOS native calendar app either)

However, are you wanting to view other's calendars to see when they're free for a meeting? The Outlook mobile apps have scheduling assistant built in, so you can find a time that works for all the attendees. Just add people as attendees, and then tap on the date or time fields to open the mobile scheduling assistant.