Outlook Online Archive on iOS

No, it's not available (unless it's changed recently), certainly from the Outlook for iOS app and I don't think the native email app can see the Online Archive. It's been requested like, https://outlook.uservoice.com/forums/293349-outlook-for-ios/suggestions/16609312-exchange-online-archive-access and https://outlook.uservoice.com/forums/293349-outlook-for-ios/suggestions/13185984-access-to-in-place-archive-in-ios-outlook-app for the Outlook for iOS app.

The only way to access it as far as I'm aware is through a mobile web browser or the OWA app, which is practically abandonware.  I guess this feature will come eventually but I have never seen it mentioned in any roadmap but who knows.

Not for me to say but it might be time for the user to simplify their workflow!