I have this iFixit guide as my source: https://www.ifixit.com/Guide/Choosing+the+Right+Screwdriver+Bit/93991#s176809 According to that, the JIS screws have orthogonal inner angles, while the Phillips’ are rounded, resulting in the slipping bits. However, some Phillips screwdrivers fill out that space, and thus won’t fully go into a JIS screw, and effectively be too small, stripping it.