Thanks. That clearly answers my question.
So, to clarify, the controller uses the WiFi to control the spark and the spark must not fly beyond the range of the WiFi. Also, line of sight must be maintained in order not to block the WiFi signal.
Depends if using only spark and phone the spark is wifi, this is why range is limited. Using the controller and phone the wifi comes from controller to phone and the signal is RC from controller to Spark giving more range.
The wifi communication is two-way, so the phone - RC - Aircraft route described above is also reversed. The point is that if an RC is used, there's no direct communication between the phone and the aircraft.