There are two sets of phonetic symbols that have the same sound in Japanese.
この場合、次のように言うと良いと思います。
ーThere are two sets of phonetic symbols that have the same sound in Japanese.
「日本語には同じ音を持つ2組の表音文字があります」
two sets of ... で「二組の…」
phonetic symbols で「表音文字」
to have the same sound で「同じ音を持つ」
ご参考まで!