Is my warranty valid in another country as where I bought the phone?

In general, the warranty is only good in the country in which the iPhone was purchased. All that you can really do is ask the Apple Store or Apple Service shop in New Zealand if they will honor the warranty on your phone purchased in South Korea.

The exception to this general Apple policy is the European Union, since a phone purchased in any E.U. country will have a valid warranty in any other E.U. country, including Switzerland.

The warranty is only valid in the country where the phone was initially sold. However, for a screen replacement you can see if a local Apple store or authorized service provider will take pity on you.

The warranty is only valid in the country the phone was purchased in. However, you could always try, they may replace it for you.