The titration curve drawn right below the explanation you posted is perhaps a better perspective! Try labeling the regions represented by each choice. That I think is the best way to look at. Without drawing the curve you can get rid of choices A and B, but you use the curve from there. If the curve in the answer explanation is confusing, you should post it and share where it is unclear.
Without using the curve, you can consider that you are dealing with H2PO4^- and HPO4^2-, which means you need to involved pKa2. You have more of the -2 species than the -1 species, so according to pH = pKa2 + log [HPO4^2-]/[H2PO4^-], you have pH = pKa2 + log [0.2]/[0.1], which is greater than pKa2. It's PKa2 + 0.3 to be exact (if you wish). This eliminates choices A and B. From here, you really do need to consider the titration curve. Choice D is saying that pH > pH at second equivalence, which can't be possible because you still have H2PO4^- in solution. Choice C is the best description.
