Conventionally most fertilizers list elemental content as if they came from a group of standard compounds, even though the compound in the fertilizer isn't one of those. I don't know why this is, and it can mislead us non-chemists.
Don't be concerned about the "Redfield Ratio", it means nothing for aquarium fertilizing. And, while you can have too much of anything we put in our tanks, you can have a lot more phosphate than we try for without any problems occurring. One proof of this is that many of us have accidentally put KH2PO4 in our tank thinking it was KNO3, so we had 4X the desired amount. I haven't read where anyone had problems from doing that. I didn't when I did it, and I routinely dose double the EI recommended KH2PO4 dosages with nothing happening that I can see, other than that I don't get green spot algae.