This works regardless of whether you access the web library on a desktop or a mobile device; however, on mobile, an extra step is required to enable item selection:
In Zotero for iOS, bibliography generation is accessible from the “share” icon when items are selected. The Android version of Zotero might not have this feature yet, but it’s coming soon.
Upgrade Storage
https://s3.amazonaws.com/zotero.org/images/forums/u3978561/6yzc4ltmw7mbjo4z38iq.png
This works regardless of whether you access the web library on a desktop or a mobile device; however, on mobile, an extra step is required to enable item selection:
https://s3.amazonaws.com/zotero.org/images/forums/u3978561/ojr5789okb6ofxs9izrg.png
Then the icon appears at the bottom of the screen:
https://s3.amazonaws.com/zotero.org/images/forums/u3978561/zp74f5x5r2l75vvu76oh.png
This feature is currently limited to a 100 items but this limitation will be removed in an upcoming version.