Will the Philippines declare martial law?

It is doubtful. I think that President Duterte suggested that as more of a rhetorical move, trying to emphasize how important his position is. On the other hand, requiring arrest warrants and acting within the law is supported by the constitution.

It has got to be frustrating trying to fight against the illegal drug trade and corruption of high officials, who theoretically can thwart legal channels, but even for the President, staying within the law is absolutely imperative, as he fights those who flaunt it.