The "2.7" mm screws are not phillips screws. The center hole is threaded to receive other screws. If you look at the previous steps, you can see the screws that screw into each one. While the instructions talk about a flat-head bit, I suspect there is a special bit for these, a "+" shaped bit, possibly with a recessed center (hard to tell without more magnification than I had.) Without that tool, the best alternate is a flathead. I would avoid using a bit in the center hole, since it may damage the threads.