Hello. I am so very sorry about your loss. Losing a family member and loved best friend is bad enough under normal circumstances, but canine kidney disease is among the worst of conditions to deal with - and yes, it can deteriorate alarmingly fast.
My initial involvement in this disease - and indeed this very forum - began after I lost my own beloved BB (a lurcher) to this horrible illness. At that time, I too was very ignorant. My own vet - who I trusted implicitly - also proved to be unfamiliar with the condition. My dog was diagnosed on Friday as she was off her food, on Saturday she became extremely lethargic and refused all food - and she passed away on the Sunday. It was a devastating three days.
After that, I vowed to learn more about the disease. That was 5yrs ago - and I now operate this forum and others (including some on FaceBook), passing on my own knowledge and gathering together knowledge and experience from others. I also write exclusively and professionally (without charge) for this forum and other doggy sites about canine kidney disease, having read thousands of study papers, research documents and so on. This is my way of paying BB back for the years of love and loyalty she gave me - it's her legacy.
I rarely blame vets for their lack of knowledge or experience. They have a huge task learning about hundreds of different illnesses, diseases and physical ailments, and for lots of different animal species. They cannot know everything, though some are more knowledgeable than others.
It would probably have been better to start a phosphate binder earlier. Of that there's little doubt. But that could only be confirmed by knowing the blood values at an earlier stage. It's the blood values that determine the best time to start a binder.
There is also nothing certain about managing canine kidney disease. Some dogs rally with good support - yet others fade away, even with exactly the same support. We can only do our best. You should have no regrets. You did your best. And more than that, you offered your dog a great life, lots of love and security, warmth and so many happy years. The end period was a very small part of your dog's long and contented life. Try to remember that.
Tony