Link to upload a file doesn’t show for SharePoint on iPAD, iPhone or Android mobiles

Seem to be having a weird issue with SharePoint on mobile. We are using the latest version of SharePoint on our server

We have a link that allows users to upload files to the server, i.e. documents or photos. It works fine on a web browser (on a PC or MAC) but, when you open it on a iPad, iPhone or Android the link disappears. Even if you switch to the PC view. Any ideas are greatly appreciated. 

thanks