Hope it is ok to bump this. I'm planning to do the landscaping this weekend and really curious for some ideas. Let me know if any other information would be helpful to add.

Oh my, that is great! Thank you so much! I think something like that would work wonderfully. I have about 4 feet to cover, do you think I should tier something taller (grasses?) behind the phlox or just let it spread all the way back?

I did put in two knock-out roses today on each corner because they needed to get in the ground. I'll get some new pictures in the morning with the fence back up.

To add to yardvaark's mix, if you can find an Exochorda macrantha "The Bride", it's perfect for spilling over walls. Doesn't get much taller than 2 feet, and the long, non rooting branches spill down. It blooms in early spring, simply covered in white. After that the blue-green leaves stay attractive all season. Mine is not on a wall, but I'm very fond of it and it's never presented any problems.

Your question about adding taller material ... I have no idea what your view is from the pool area. Are you trying to screen something? If the view is great, maintain it by keeping the plantings more or less low. If there's something you don't want to look at, figure out where to put some ornamental grasses that will screen.

Let me add some more recent photos that will explain. The privacy fence wasn't present in the original. The view will be blocked by the fence, so the landscaping on top of the retaining wall is only visible from the outside. And the width is closer to 6' instead of the 4 i mentioned earlier.

Also included bonus shot of view from inside the fence.

Rosemary?
Trailing juniper?

Where are you? Zone 6 is just how cold it gets.

I'm in East TN valley/foothills. Noticed yesterday that the bed was still getting full light around 4pm over the fence.

In that case, I'd plant taller material -- in whatever artistic arrangement works -- at, and near, the ends of the run, and shorter and trailing material nearer the center of the run. It might help if you thought of it as a cross-section of a stream where the ends of the run are the banks and the center is the flowing stream. Where we "cut through" it for the x-section, the water begins to spill over the cut.

Don't forget to think of what it will look like in the winter. When the sun is shining it is easy to forget that there are days that it doesn't.

Pampus grass in the back along the fence and phlocks in the front?

and some oversized pots placed throughout with annual flowers for a splash of color.

Pampas grass is not zone 6 hardy, but there are lots of great grasses that are.

Look at Miscanthus species, Muhly or fountain grass.

My 2 cents:
Hydrangea arborescens 'Annabelle'. Naturally floppy but would look great cascading over edge of wall. Mix with some evergreens, but not pointy ones, in my opinion, go for moundy.

Or, plant Hydrangea petiolaris (climbinb hydrangea) at the base and let it climb up and cover the wall.