The Philistines appear only within Nephi’s quotations of Isaiah. In a rebuke of the house of Jacob, the Lord is said to have forsaken his people because they hearken to soothsayers like the Philistines and please themselves in the children of strangers (2 Nephi 12:6).
In a prophecy of judgment on Israel, the Syrians are placed before and the Philistines behind, the two together set to devour Israel with open mouth (2 Nephi 19:12). A later passage reverses the relation: the gathered remnant will fly upon the shoulders of the Philistines toward the west, spoil the people of the east, and lay their hand on Edom, Moab, and the children of Ammon (2 Nephi 21:14).