Best low phosphorus dog food?

My oldest dog is almost 12. She was just diagnosed with early stages of kidney disease.

My vet recommended putting her on a low phosphorus/low protein diet and has ordered me a bag of Royal Canin rx food for kidney health.

I know RC overall isn't that great of a food, but have heard their rx food is pretty good.

Being my dog is in the early stages, the low protein isn't as important as the low phosphorus.

So, I'm looking for options that may be better than the RC.

I saw a Wysong Synorgon that looked pretty good.

Any other suggestions? Ideas?

Yes, I do plan on talking to my vet more this afternoon. They were swamped when I had my dog in there a couple days ago and I needed a couple days to do some research to come up with some questions and ideas to go over with her.