I flipped through Schachter's Harmony text the other day, and of course, so many examples of "proper" chord progressions use example from Bach's chorales, which are mostly (if not all) based on 4 voices. He emphasized a lot about how even the bass line needs to make sense, i.e. no big leaps unless necessary.
And now I think I realize why my grandma and Eugene told me on separate occasions that I need to pay more attention to my left hand. I haven't been paying enough attention to the base line because I have thought of it as little more than mere chords that support the melody in the right hand. But apparently, in a masterpiece--which is pretty much any classical music that is worth playing in modern day--bass lines are important.
Schubert's impromptu (op 142/2) was used to illustrate various V7 chord inversions. These inversions allow for varied bass line. I don't think I really thought of them that way before.
Anyway, so in addition to phrasing the top line, I need to pay attention to the phrasing in the bass line as well. And of course, this extends to the middle voices as well.
All this requires developing a better ear, which I'm trying to do alongside also.