There is a known problem relating to Add-ins on mobile devices (iOS or Android), which appears to originate with Microsoft's own servers. 

Whilst you may have enabled the Add-in via Outlook desktop, and you can even see it in the list of enabled Add-ins on your phone, when you try to invoke it via the triple-dot menu, it's not offered or possibly appears but without an icon.

This appears to happen when there is a synchronisation delay.

Close Outlook on your mobile and restart it then try again. It may not work immediately but will eventually appear, sometimes as much as a day later.

SUPPORT FOR MOBILES: If staff already have access to their emails and calendars via mobiles and tablets, there is nothing extra required and CloudFiler should work fine. If however you have yet to enable mobile device access to Exchange, you will need to do this by following Microsoft's guidance Clients and mobile device permissions in Exchange Server

CloudFiler works in the Outlook App but not in your browser

Microsoft do not allow Add-ins to load in their Outlook Web Access (OWA) client when running on mobile devices; they expect you to use their Outlook App instead.