You made me care about a character I knew nothing about within the span of [checks watch] two minutes, so congrats!
This is interesting as a short piece. It does feel like a mini-game to promo a bigger work, or as one part of a bigger game or ARG. The slow dawning of realization coupled with the brisk cutoff of the end was a good combination.
Some suggestions:
- Have the sidebar stowed, it takes up a lot of the screen without much use.
- The audio adds to the feel, but this specific track is kinda grating. A different sound might work better.
- A bg that's just an image of a phone rather than something that describes the pocket dimension (the Silent Hill style of text overlayed on an image of a letter to denote that you're reading it, kind of thing). While the current bg isn't distracting, it's a representation of the location rather than the phone call itself, and since the player doesn't know what the pocket dimension is, using a different bg might fit the theme a little better.