They represented consonants in the Egyptian language, but by convention we now read them as vowels. 𓄿 was probably a glottal stop, 𓇋 was probably like the y in yet. https://en.wikipedia.org/wiki/Egyptian_language#Egyptologica...

It also seems possible that they were sometimes used to stand for vowels even in real Egyptian phonology, in the same way that certain consonant signs are used in Hebrew and Arabic https://en.wikipedia.org/wiki/Mater_lectionis