The use of this Phoenician letter for just a vowel seem is a result of the early Greek alphabets, which adopted the letter "omicron" to depict the vowel /o/. The letter was adopted with the value within the Aged Italic alphabets, such as the early Latin alphabet. Good Vocabulary: https://rylanenuyc.alltdesign.com/the-basic-principles-of-o-sapinho-e-a-borboleta-55992226