They didn't charge you. The explained already what they did, as you yourself say. They put a hold on your credit card in the amount of the replacement in the event that you do not return your original iPhone. The hold will be released when they receive your original iPhone. This is also explained very clearly in the information for the Express Replacement Service:
When you request Express Replacement Service, Apple places a reserve on your credit card for the Replacement Value of a new iPhone. This covers any damage to or loss of your iPhone that is not covered by Apple’s warranty or an AppleCare service contract and/or other payments that may be due. If the replacement of your iPhone is determined to be covered by Apple’s Limited Warranty for iPhone, you will only pay the ERS Fee shown in the table below. This fee is waived if your iPhone is covered by an AppleCare service contract.
If you do not understand what a credit card hold is, see:
So no, you do not have a dispute and will not unless Apple doesn't release the hold once they get back your original iPhone.