Nexus 5 "Phone Search" is completely blank -- how to add information sources here?

[AC Question]

Subject says it all: when I go to Settings -> Google -> Search & Now -> Phone Search, I get a blank screen. It just says "Phone Search" at the top, with a left-pointing (back) next to the heading. Otherwise the screen has no content.

How do I enable this feature so that I can search my phone for contacts, songs, apps, etc.?