With the following campaign types you can specifically target your audience by mobile device, because the ads will be running on mobile only:
- Mobile App Install
- Mobile App Engagement
- Any other campaign type with no Desktop placements selected
On the Audience step (3) of campaign creation, for the campaign types listed above, a Mobile Devices targeting section is available. Here you can target iOS or Android users specifically, target by device version, type, and even whether the user is on Wifi only.
For campaigns that aren't running just on mobile, but have mobile-related offers to display, there are similar mobile targeting options within the Detailed Targeting section. Click Browse, and then select the Behaviors folder. You'll find several Mobile Device User folders to choose mobile targeting options from.
See how to target a Facebook audience.