http://www.ryanair.com/en/questions/mobile-boarding-passes/
However, you must be using an ID issued by an EEA country (ie you don't require a "visa check") and they are not available from the following airports:
Agadir
Essaouira
Fez
Nador
Oujda
Marrakesh
Rabat
Tangier
Zaragoza
Alghero
Rome Ciampino
Kefalonia
Volos
If you have checked in online you can retrieve your boarding pass on your phone, but you will need a connection to do this. Otherwise it is stored on your phone, and can be retrieved at any time.
Mobile boarding passes can be used on bookings with multiple passengers.