Reincarnating In Another World With My Smartphone

What happens if you were suddenly reincarnated in another world where magic exists, where mythical creatures like dragons, dwarves, elves and demi-humans lives, and the only thing that you have is your smartphone? Rubi Red, a 20-year old college student working in a fast-food restaurant as a part-time crew is walking exhaustedly to the train station after his work, busy with his smartphone for status update in social media when suddenly notices that someone is in danger. A woman close to his age is being robbed by a man with a knife. Rubi rushes through the scene to save the woman but unfortunately Rubi has been stabbed. "I don't wanna die.", his last post in his social media. After making flashbacks, a gently voice whispher to his ear, saying "Come with me...". Rubi suddenly wakes up in a forest where unexplained creatures exist. The only thing that he has is his undying smartphone. Rubi wondered around the forest and saw the woman who he saved before reincarnating. Rubi hides himself when a group of royal guards came. Rubi follows them unnoticeable and saw a vast kingdom. Rubi's smartphone suddenly vibrates and tells him, "Welcome to the kingdom of Elsia". Walking down the hill exhaustedly, he met an old man and asks for a ride. Inside of Elsia, the old man offers Rubi a job as a waiter in a beerhouse. Rubi gratefully accepts the offer. Several days later Rubi saw a hooded person passed out and tries to wake the person but suddenly guards came in looking for someone. The hooded person drags Rubi outside. And turns out, the hooded person is the woman who he saved before reincarnating. Rubi's smartphone suddenly vibrates and tells him, "Risaline Elsia". Rubi notices that the woman he saved is actually the princess of the kingdom. Risaline asks Rubi as her knight to defeat the demon armies. Risaline explains to Rubi that she is the one who reincarnated him and tells Rubi that he has superpowers and one of it is immortality like his undying smartphone. What will Rubi's gonna do in another world where the only thing he has is his smartphone?...