I don't know if you've ever heard the term "phrasing" applied to singing, it's not something you hear often anymore. To be honest its not something I'm sure I can define. The closest I can come to is that it refers to a singer's ability to associate the lyrics of a song with the music. However, it means more than just being able to carry a tune. It's how you sing the words and music together. It's the ability to turn your voice into a lead instrument in a band and take one word and extend it over a whole series of notes. However ,it doesn't just mean the ability to sustain a note. It's continuing to sing the melody, but with only one or a few words without them losing meaning or throwing the continuity of the song out of whack.
Listen to Vaughan wrap her voice around a word and you begin to understand what is meant by the term. You also realize why you don't hear the term used very often anymore as very few modern singers have this ability. To be fair the music of today doesn't really lend itself to that style of singing either. However hearing a singer of the quality of Vaughan, you begin to regret its passing. I'm sure there are jazz singers around who have the ability, but we don't hear them on a regular basis.
Of course it's this ability which allowed her to be equally comfortable with any style of music she wished to sing. On After Hours we hear her sail through a series of smoothly orchestrated pop tunes. Even the version of Gershwin's "Summertime" on this disc is given the uptempo treatment. This might have been a collection of rather commercial standards, but she gives them a soulfulness that raises them above the level of just another pop song. She might not be as emotionally raw as Billie Holliday, but that doesn't stop her from being able to imbue even the simplest of songs with the heart necessary to make them soar.