Would the mechanism for the reaction be polar or radical?

[![Reaction which the question is based upon.](https://i.stack.imgur.com/57KJZ.png)](https://i.stack.imgur.com/57KJZ.png)


I've disregarded the fact that the reaction could proceed via a concerted mechanism but am unsure how else it would go.


My thoughts are that it either goes via a polar mechanism or a radical mechanism. Where in the polar mechanism, the reaction would proceed via electron transfer between charged intermediates. In the radical mechanism, the formation of nitroso and phosphine free radicals would drive the reaction.


I'm leaning towards polar due to the reactivity of the nitroso and the strong polar nature of the system but unsure about the rate determining step and whether it would be addition/elimination (N=P formed first then N=O broken) or elimination/addition (N=O broken first, N=P formed after).


