The Apple Pencil was specifically designed for the iPad Pro and does not work with any other Apple devices. Apple's website doesn't explicitly say the Pencil only supports the 12.9-inch tablet, but it does indicate several times that the Pencil is exclusively an iPad Pro accessory. The iPad Pro display was created to work with the sensors found in the Pencil tip and none of its advertised features will work with the iPhone 6s, iPhone 6s Plus, and older iPhone or iPad models. This includes the iPad Air 2 and iPad mini 4.
Does the Apple Pencil work with the iPhone 6s / iPhone 6s Plus?