When you use Yammer on a mobile browser on an iOS device, such as an iPhone or iPad, you cannot upload and attach files to your posts.
This behavior is by design.
Yammer focuses on delivering a rich native app experience on mobile devices
To work around the issue, install the Yammer iOS mobile app that supports uploading and attaching files to your post.
Article ID: 4035416 - Last Review: 2017, ജൂലൈ 18 - Revision: 12