No, if you get off in NRT, they’ll cancel the remaining legs, including the return legs, of your ticket.
Fares are calculated origin to destination and NYC-TYO is seen as a different market than NYC-MNL. The connection in TYO is irrelevant.
What you can see is if there’s the ability to do a stopover in the MNL ticket. If so, you could do
NYC-TYO-stopover in TYO-MNL-TYO-NYC.
This may be cheaper than just the 2k ticket, plus you get some more miles out of it.