The Ancient Egyptian writing system had a set of some 24 hieroglyphs that are called uniliterals, which are glyphs that provide one sound.
ðɪ ˈeɪntʃənt ɪdʒˈɪpʃən ɹˈaɪɾɪŋ sˈɪstəm hæd ɐ sˈɛt ʌv sˌʌm twˈɛnti fˈoːɹ hˈaɪɚɹəɡlˌɪfz ðæt ɑːɹ kˈɔːld jˌuːnɪlˈɪɾɚɹəlz, wˌɪtʃ ɑːɹ ɡlˈɪfz ðæt pɹəvˈaɪd wˈʌn sˈaʊnd.