One unique feature could be the concept of modern technology like a smartphone existing in a different world. It might bring about unexpected interactions with the different world's magic or social systems.
The 'smartphone in another world' novel may have the unique feature of exploring cultural clashes. The smartphone, which represents modern Earth culture, enters a world with its own distinct culture. This can lead to interesting situations where the values and functions of the smartphone are either embraced, misinterpreted, or even feared. For example, the camera app might be seen as a magic device that steals souls in a superstitious world, or it could be a way to document new species and landscapes in a more scientific - minded other world.