How to edit documents in SharePoint app on iPhone?

Hi,

Not sure if this is the correct forum for this kind of question but here goes.  I am using Intune to manage our fleet of iPhones and pushed the SharePoint app out to a group of user's phones.  It seems to be working fine with the exception that they can't seem to edit documents from the phone.  They can edit documents from a computer so I believe the licensing is right.  

Is this something they should be able to do?  How can I give them the ability to edit the documents, do they also need to have Word or Excel installed on the phones as well?

Thanks in advance!