phonetic form
Technical term in linguistics referring to the spoken or sound-based representation of a word or utterance, as opposed to its written form.
We investigate the correspondence between phonetic form and written form.
表記 refers to written representation or notation, while 音声形式 specifically denotes the spoken or phonetic form.
Compound of 音声 (onsei, 'speech sound') and 形式 (keishiki, 'form'). The exact historical derivation is uncertain, but the term is a modern technical coinage in linguistics.