A mobile device is used as an input/output device for a player tracking system for gaming machines, such as slot machines. Each gaming machine has a unique identifier and each player has a unique identifier that is associated with an account of the player. Player credentials are electronically communicated via the mobile device directly to the player tracking system, and each player credential is associated with a player's unique identifier that is maintained by the player tracking system. The mobile device is also used to electronically communicate directly to the player tracking system a gaming machine that the player wishes to play. Prior to initiation of game play on a gaming machine, the player tracking system associates the unique identifier of a player with the unique identifier of a gaming machine that the player wishes to play. A play session is initiated at the gaming machine and game play at the gaming machine is associated with the account of the player, and activity from the play session is captured by the player tracking system. Information is displayed on a display screen of the mobile device during the play session, including data regarding the player that is maintained in the player tracking system.