${\mathrm{P}}_4\left(s\right)+3{\mathrm{OH}}^{-}\left(aq\right)+3{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)⟶{\mathrm{PH}}_3\left(g\right)+3{\mathrm{H}}_2{{\mathrm{PO}}_2}^{-\left(aq\right)}$ For this reaction, the oxidizing and reducing agents are, respectively :

Since the given reaction is a disproportionation reaction ${\mathrm{P}}_4$ will be the oxidizing and reducing agent.
${\mathrm{P}}_4\left(\mathrm{s}\right)+3{\mathrm{OH}}^{-}\left(\mathrm{aq}\right)+3{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)⟶{\mathrm{PH}}_3\left(\mathrm{g}\right)+3{\mathrm{H}}_2{\mathrm{PO}}_2^{-}\left(\mathrm{aq}\right)$ 
Hence correct option is D.