phonetic symbol vs grapheme

phonetic symbol and grapheme both are nouns.

Word	Noun	Adjective	Verb	Adverb
phonetic symbol	Yes	No	No	No
grapheme	Yes	No	No	No

As nouns, grapheme is a hypernym of phonetic symbol; that is, grapheme is a word with a broader meaning than phonetic symbol:

phonetic symbol: a written character used in phonetic transcription to represent a particular speech sound
grapheme: a written symbol that is used to represent speech

Other hypernyms of phonetic symbol include character, graph, graphic symbol.

phonetic symbol (noun)	grapheme (noun)
a written character used in phonetic transcription to represent a particular speech sound	a written symbol that is used to represent speech