As long as the iPhone charger is a microUSB, not a 30 pin connector. If the phone normally draws about 1200mA (
Galaxy Charging Current Lite will tell you), it'll take a little longer to charge from the same point with a 1 Amp (1000mA) charger - about 1.2 times as long. (As long as the charger can supply about 10mA, it'll charge the battery. It may take days, but it'll charge it. And if the charger can supply more current (I usually charge my phones from a 20 Amp supply), the phone will draw only as much as it's designed to.
Basically, you can use any 5 Volt microUSB charger to charge any device that uses a 5 Volt microUSB charger. (5.2 Volts - which is how Samsung rates their chargers - is fine too.)
Apple may have violated a ton of standards (iMessage, iPhone emojis, etc.) but not even Steve Jobs could figure out how to violate the laws of physics. (Maybe he can now, but it's too late to tell us how.)