It's perfectly possible to charge an iPhone with an iPad charger, and it won't hurt either the iPhone or the charger. The iPhone charger can also charge the iPad, but it takes longer to charge. iPad and iPhone chargers are designed differently for a reason. The iPhone's battery capacity is small, requiring only 1A charging current to complete the charge in a reasonable time. Although the larger charging current can greatly shorten the charging time, it will bring more heat, and high temperature is the number one killer of lithium battery life reduction, so the maximum output current of the iPhone charger is designed to be 1A. The charger of iPad is marked with 5V 2.1A, which means that the maximum output current of the charger of iPad can only be 2.1A. When you use the iPad charger to charge the iPhone, although the iPad charger can provide A maximum of 2.1A current, but because the iPhone can only accept 1A current, the iPad charger only needs to accommodate it. The iPad's battery is designed to charge at a current of 2.1A for the best charging time. If you use the iPhone charger to charge the iPad, because the iPhone charger can only provide a maximum current output, the entire charging time will be 2.1 times. Because of Apple's trick on the USB port data pin, the iPad knows that this is an iPhone charger, and will not \"require\" more than 1A charging current, and will not overload the iPhone charger and cause damage.