Maybe some more phlox in muted shades? Or shades of pink and white phlox? Deep purple cosmos would also make a nice contrast if you use the white as filler.

Or you could do a few all white bouquets and add more white flowers in varying shapes like the seashell cosmos and white zinnias. You could accent the white bouquets with some dramatic dark green leaves for contrast.

I Have Echinacea blooming with phlox. Just the ordinary pink type, but they look nice with phlox. I also use Molucca, Bells of Ireland, I like the columnar form with open phlox.