Don't worry about the phone's charging amperage. The phone determines the amperage because it "looks" at its mircoUSB connector's data pins. When the phone detects that the charger has the modifications like a Samsung charger then the phone will charge rapidly with its max allowed amperage. Without detecting the modification, the phone will draw just trickle charging amperage, meaning about double time for charging.
Your iPhone charger might have this modification or it might have not ... in each case it won't harm your phone