The game is a tamagotchi like, to complete the digimon encyclopedia you need to have those digimon. Multiple digimon at the time is kind of difficult to implement with the current system, the phone mimics a digivice like you have your partner digimon, these mechanics are taken from the DW1 game. A digimon full lifespan is no more than a month tops. Then it transforms into a digimemory.