When you hear the word phrasing, what do you think of? Long lines, where to take a good breath, crescendo- decrescendo and timing, to name a few things that might enter your mind on hearing that word.
To me the structure of the phrasing is determined by the character and spirit of the music. Like anything else, it is easy to play with a method of phrasing that can make our music making sound controlled and well placed. Those are all useful aspects to phrasing. But in the end, if your phrasing has a formula to it that doesn't alter according to the different kinds of music, then that nicely timed, well placed phrasing can sound out of place and not in character with the actual music.
To approach this, let's look at horizontal and vertical. The long linear aspect of the line makes most of us think horizontally, like looking at a horizon. It is broad and covers a lot of space. In music, this long sense of line gives direction, motion and balance to all the up and downs, curves, peaks, valleys and hills in a line. But if we 'flatten' it out too much, we can loose the emotional and character details that create the nuances that identify one kind of phrase from another.
What about a singer? They use words. If you could not hear the diction of the words it would sound muddy and nondescript. As wind players, we think of 'singing' through the horn to help us unify the musical and technical aspects together. But we are not often thinking of the diction and nuances beyond smooth, legato, pretty lines. Certain things a cellist, singer or oboist do in terms of inflections (vertical aspect) are not oftentimes accepted very well by the orchestral trombone community at large, especially with regard to orchestral excerpts.
Listen to people speak. How horizontal is their phrasing in speaking? Listen to instrumentalists. How much vertical nuance is there as compared to the line length (horizontal aspect ) in their phrasing? What about percussionists? Are there different vertical and horizontal phrasing tendencies for different instruments?
What are your tendencies in this area? Listen to others and get a grasp of what is horizontal and vertical in phrasing. Then record yourself and see how balanced your horizontal and vertical aspects are in your phrasing. It is an interesting and rich territory for those who may be interested.