PhoneticEncoding

The phonetic encoding of the phrase.

Enums
`PHONETIC_ENCODING_UNSPECIFIED`	Not specified.
`PHONETIC_ENCODING_IPA`	IPA, such as apple -> ˈæpəl. https://en.wikipedia.org/wiki/International_Phonetic_Alphabet
`PHONETIC_ENCODING_X_SAMPA`	X-SAMPA, such as apple -> "{p@l". https://en.wikipedia.org/wiki/X-SAMPA
`PHONETIC_ENCODING_JAPANESE_YOMIGANA`	For reading-to-pron conversion to work well, the `pronunciation` field should only contain Kanji, Hiragana, and Katakana. The pronunciation can also contain pitch accents. The start of a pitch phrase is specified with `^` and the down-pitch position is specified with `!`, for example: `phrase:端 pronunciation:^はし phrase:箸 pronunciation:^は!し phrase:橋 pronunciation:^はし!` We currently only support the Tokyo dialect, which allows at most one down-pitch per phrase (i.e. at most one `!` between `^`).
`PHONETIC_ENCODING_PINYIN`	Used to specify pronunciations for Mandarin words. See https://en.wikipedia.org/wiki/Pinyin. For example: 朝阳, the pronunciation is "chao2 yang2". The number represents the tone, and there is a space between syllables. Neutral tones are represented by 5, for example 孩子 "hai2 zi5".