Bunk.Is has been shown insufficient phosphorus supply will harm corals after a short period of time, insufficient nitrogen supply will harm corrals only after a much longer period.
Nitrogen and Phosphate levels in wild, healthy reefs are beyond decimal points of detectability. They cause problems in captive tanks because captive tanks acclimate corals to nutrient levels a million times higher than the open ocean and then the coral has problems when you cut off the fertilizer. Just look at the number of fish in the average 125gallon tank -vs- the ocean. Even a low nutrient tank has piles more fertilizer and P04 than a healthy wild reef. Grown plenty of SPS in fishless tanks.
Also, if Po4 were required for SPS growth it would be present in coral skeletons which it isn't.