That would be a question you would need to take up with the taxing entity where you intend to buy your iPhone. The process is not the same in all EU countries. You also probably need to talk with whoever will be financing your phone. They may insist that you apply any refund to your loan balance, or may insist on applying for the refund themselves (though I don't know if that's possible).
I would, however, strongly caution you about buying an iPhone outside of the country in which you're actually living. The warranty on an iPhone is not international, so if something were to go wrong with the device, it's quite possible that you would not be able to get service on it locally.
Regards.