Can I use a stylus with the iPhone X?
The iPhone X does not support the Apple Pencil. The Apple Pencil is only supported by Apple's "Pro" iPad models. This includes the 9.7-inch iPad Pro, 10.5-inch iPad Pro and both generations of the 12.9-inch iPad Pro.
There are plenty of third-party styluses that claim to work with all touch screen devices, including the iPhone. There are no Apple designed styluses for the iPhone X at this time.