Titration question...

Email question:
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I am having trouble with this question from a previous exam: You find that 25.00mL of phosphorous acid requires 41.39 mL of Sodium hydroxide to reach the second equivalence point. What is the concentration of the phosphorous acid solution?

I understand the process of what to do in this question, but am really struggling understanding why we are supposed to use the equation that you used in the explanation: H3PO3(aq) +2 OH-1(aq)†(一)2O(l) +HPO3-2(aq)
Earlier in this problem, we broke down this into three different equations, and I don't understand why we don't use 
H2PO3-1 + OH-1 --> H2O + HPO3-2?
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The equation you list gets us from the first equivalence point to the second equivalence point. In the titration described in the equation, we're going from phosphoric acid all the way to the second equivalence point, so we're doing 2 steps of the potential 3 step process. To get to the second equivalence point, have to go through the following steps:
H₃PO₃(aq) + OH^-1(aq)(aq) <=> H₂O(l) + H₂PO₃^-1(aq)

H₂PO₃^-1(aq) + OH^-1(aq) <=> H₂O(l) + HPO₃^-2(aq)

So the whole 2-step process to get from the beginning of the titration to the second equivalence point has the net equation:

H₃PO₃(aq) + 2 OH^-1(aq) <=> 2 H₂O(l) + HPO₃^-2(aq)

That's where the 2:1 stoichiometry comes from.