I started using Rowaphos and I agree it works immediately but if you have a lot of phosphate you may need to change is quickly to start with as it becomes spent. Also maybe try using a bit more in the reactor so you don't need to change it as often
When I started using it my phosphates were way lower than yours at 0.16 and I had to change it after just 3-4 days to start with. I had been in touch with DD about a combination of things and they said just use extra to avoid changing as often in my size tank (i used double amount) until things are under control as you can't overdose on it.
You just need to test regularly as above the reactor out water and tank water and that will tell you when to change it and eventually once all phosphate has leached out of the rocks etc it should come down to
Having said all of this, also bear in mind that depending on what corals you have etc., it may be better to reduce phosphate slowly in case the corals have become accustomed to those high levels rather than a sudden reduction as they can be very sensitive.
My tank runs now at around 0-0.04ppm on both Red Sea Pro and Hanna test kits and I'm using around 500g Rhowaphos in a Deltec FR509 reactor for a rough actual water volume of 575litrs (Red Sea Max S650) and at the moment change the Rowaphos about every 4 weeks
Due to test kit inaccuracies and also feeding, your unlikely to have 0 phosphate even though a test kit says that, and also you don't necessarily want 0 Nitrate or phosphate as the water will be too clean and sterile.
So basically sounds like you need to change it, and then change more often, and it will work as it's very effective.