This was a very interesting concept for a narrative game. For the most part, puzzles were logical and easy to trace out.
I actually had the most trouble with the initial PIN. I assumed that the hint was suggesting some permutation of day/month/year for the birthday instead of just the four-digit year. Not sure how to prevent overthinking on that one. If you want to make it more forgiving perhaps you could make the game quietly accept a few alternative solutions?
While I get that the battery level mechanic was included to incorporate the jam theme, I felt it was mainly a source of frustration when trying to explore the contents of the phone thoroughly.