How can I convert UTF-8 encoding to gbk simplified?

How does php convert UTF-8 encoding to gbk simplified? As the question. I will convert the traditional big encoding to simplified ones ., Then we need to convert big5 to simplified and complex conversion, and use mb or iconv for encoding conversion. how does php convert the traditional UTF-8 encoding to gbk simplified?
As the question. I will convert the traditional big encoding to simplified ones.
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Switch to big5 first.

Simple and traditional conversion requires a code table. the encoding is converted to mb or iconv.