Phase 2 - what the blooms look like after the white feathery phase

That doesn't appear to be an Endless Summer. It looks more like an arborescens to me. Where did you get the shrub (garden center, start from a friend, plant sale, etc.)?

Looks like a wild hydrangea. Here is a shot of a wild one from two weekends ago in some state park in TN.

A landscape designer included an "endless summer" in our plan. The landscaper put it in. I'm such a novice that I don't even know -- I'm just going off of the design schematic and assumed what I have is what is on the plan! Any idea what I can do to resolve the problem? If it's too late this year, I want to be ready for next year. Thank you! :)

Go back to your landscaper and tell him/her you didn't get what you paid for and see if they will fix it. If they don't fix it then you can dig out these hydrangeas and put in what you want. I was at our local HD this morning and saw they had Endless Summer, Blushing Bride, Wedding Cake, Limelight, and maybe a few more. A lot were half price. The biggest issue I see at HD is they squeeze all the pots together which makes it hard to select and not good for the plants either.

It's only a problem if you don't like the plant. There is nothing wrong with it - that's just the way it grows and flowers. But if you were hoping for an Endless Summer, then I agree going back to the landscaper and asking him to correct the mistake is appropriate.

Looks like you're dealing with something like H. arborescens 'White Dome'