You can't stop a remote erase command. If you have the phone you can try quickly putting it in airplane mode in settings before the remote erase is executed, then back it up in itunes, turn airplane mode back off and let it erase, then restore the backup your made earlier.
If you don't have the phone there is nothing you can do yourself. You could try contacting iCloud support to see if they can cancel it but I'm not sure they can.