What policy?
Apple discontinued the iPhone 5s, so they no longer make them, nor sell them.
You can purchase unlocked iPhones from apple.com as long as apple continues to make them, and sell them on their website. They currently make and sell iPhone 6s, 6s Plus, 6, 6 Plus, and SE.
You will need an american credit card with an american billing address, and an american shipping address as well if you wish to purchase from the Apple's US online store.
Apple also has online stores for other countries. You can check to see if Apple has an online store for the country you wish to use the iPhone in. Again you will need a credit card issued in that country with a billing and shipping address in that country.
More importantly, the iPhone's warranty is only valid in the country of purchase. so if you buy an iPhone from the U.S. online store, and take it to another country, if anything happens to the iPhone that requires service, you will need to physically return the iPhone to the U.S.