[Alexander Givental]

OK, in engineering, problems are often solved by rethinking the initial set up (the solution is then called "invention"). In math, problems are to be considered within the given, and somewhat idealized setting. In particular - no cheap cheating, such as "ah! reflections are not real iPhones", or "there could be other people with iPhones in the room", or "the hand blocks the view", or "in modern art the angles between the walls don't have to be 90 degrees", or "if I close my eyes ..." - no, the situation is meant to be the most natural (and I did see such an installation in a museum), and the question, of course, is about the number of my iPhones I see, including the reflections and the actual one.

Roger, by "both walls" I mean that at the corner of the room, (of course, parts of) the walls and the floor are mirrors - in other parts of the room, some other modern art pieces are positioned.

Allen, my answer cannot be wrong, since I haven't given any one yet. You and Carl gave the same answer, 4, but for different reasons: you - that there are 3 reflections, one in each of x-,y-,z- planes plus the actual iPhone, and Carl - based on the poems.
Carl, could you please clarify how the poem gives 4?