At the strength of the NPA during 1986-1992, they only had 1/5 of the size of the Citizens Armed Geographic Unit. They don't even have suppliers from abroad since both the Warsaw Pact and the PRC stopped supplying them weapons at the time of People Power. The only source they had was from Libya and North Korea, but in OTL this weapon supplies did not matter much. The NPA as far as OTL could not even control an island or a town here in the Philippines.
The Philippine Armed Forces as shown here assumes that it is an all-armed infantry force. It does not mention armor and air assets. Heck, even the Philippine Constabulary and the Integrated National Police could quell the NPA rebellion. Also, the NPA would have found enemies among the MILF and the MNLF and Christian militias in Mindanao.
Lastly, I want to point out that the United States will not turn tail away from their allies in Asia. The close relationship between the Philippines and the US would implore intervention, especially since this takes place during the Reagan Administration.