So I see many people asking if they could use their iPad charger, to charge their iPhone. This is a good question and the answer is yes. The difference is the iPhone charger is 5w and the iPad charger is 10w.
The benefit of charging with the iPad charger is that the iPhone will charge quicker. You can also charge your iPad with your iPhone charger, but just the opposite will happen and it will take longer to charge your iPad with your iPhone charger because it is only using 5w instead of 10w.
Also, despite what you may read elsewhere it is 100% safe to swap chargers between devices to only have to have one charger plugged into your wall. If you have both, you may as well use the iPad adapter to take advantage of the slight speed increase in charging. The iPhone will only use as much power as it needs and will not be overloaded.