A client shared this issue with me a couple of weeks ago and Autodesk has acknowledged it as a bug. If you've already installed 2018.1 it has been patched, so the scary bit that follows has been dealt with.
The issue: Place the first node of a wire and then cancel (press ESC key for example) before placing the second node. Afterward, people find that their project's Phases are no longer available. In other words, the phases are not listed in the Phasing dialog box nor in the Phase parameter for elements, when examining the Properties palette. Also, the buttons that allow us to create new phases are disabled in the Phases dialog.
Bad bug! Fixed in version 2018.1.