President Rodrigo Duterte is a student of geopolitics and he always understood the value and the importance of the Philippines' geographic location.
The importance of the Philippines to the United States for them to maintain its power and dominance in the region cannot be underestimated. Duterte understood our country's value and he also saw the how important we are to China. This is where some of Duterte's misgivings about the US is rooted. Although we have been a loyal ally of the United States, they have not given us the "value" and "importance" we deserve.
China is very insecure about its access to the Pacific which is blocked by US allies. Should there be a state of war or trade embargo, China will be trapped. They have to find a way out.
In the north, China's access to the Pacific is blocked by Japan and Taiwan. In the south, the Philippines blocks them. In the event of a conflict between the United States and China, the US allies in the region can easily choke them.
If the Philippines becomes neutral, the Chinese will have safe passage for its ships or aircraft so it can continue to trade with the rest of the world. As of now, the United States dominates power in the region and they can easily strangle the Chinese whenever they want to.
Duterte's move to make the Philippines a neutral country will punch a hole in the US's Asian defense alliance and alter the balance of power.