Thai duty-free shops don't sell Apple mobile phones, because there is no Apple store in duty-free shops. If you need to buy an Apple phone, you can buy it in major shopping malls in Thailand. There is an Apple store in the mall, and the price is cheaper than that in China. Just use your passport to open a tax refund form in the mall, and then apply for a 7% tax refund at the airport when you leave the country.