Looking up weights and DNA structures and such things in humans in wiki articles, I have calculated that 0.5% - 2% of the phosphorus in the human body is used i

Looking up weights and DNA structures and such things in humans in wiki articles, I have calculated that 0.5% - 2% of the phosphorus in the human body is used in DNA. It seems reasonable to me that it would be at least within an order of magnitude of 1% in plants as well. For this reason I doubt the phosphorus in DNA would make a significant contribution to evolving a shorter DNA sequence.