phonetic symbols are symbols for recording phonemes, and they are symbols for writing phonemes. Its principle is that a phoneme is represented by only one phonetic symbol, and a phonetic symbol does not only represent a phoneme (diphthongs is composed of two phonemes, as opposed to a single vowel.
The phonetic symbol composed of two phonemes is called diphthongs), such as Chinese phonetic alphabet, English Webster's phonetic symbol and international phonetic symbol.