There are a few apps available to help optimize using Zotero on a mobile device. This list is ever-changing, simply search for "Zotero" in Google Play or the iOS App Store to find available apps. Also see the Zotero support page for mobile devices:
Also note that Zotero.org is a mobile-friendly site, so if you just need to check a citation or join a group, you can do that with your mobile device.