Brazing using BCuP5 filler

I am having ASM handbook on 'Welding & Brazing' Volume 6, 8th edition. I am refering the handbook to know more about brazing. Currently we are brazing an ETP grade Copper strip (2.5 thick) to a spring steel strip (thk 2mm) plated with 60-70 microns of copper using BAg-1 series filler metal. Since this filler alloy is costly & production is huge, we are thinking of replacing it with BCuP-5 filler metal (after referring the handbook). As I have already mentioned the steel strip is already plated with copper, so basically the brazing is of ETP copper to pure copper. As you know BCuP series filler metal is not good for steel materials as it forms Iron Phosphide (which is brittle). But, there are some examples in the handbook, where Copper plating of 3 to 5 microns is used, so that BCuP5 filler can be used for brazing (but the plating is done on bronze). Still, I just want to confirm, whether this will work. Pls advice.