I've attempted to search for other questions answering this, but keyword ambiguity is working against me.
On my Galaxy Nexus, my battery drains rather quickly. Very frequently, when viewing the battery use details, the "Phone" item is the second-largest battery use after Screen. Items such as Cell Standby use much less. This happens even on days when I do not make any voice calls, so I'm not certain what this could be.
Is there something I can do to reduce this battery drain? What causes "Phone" to use this much battery?
edit: Here's a screenshot demonstrating what I'm talking about. I don't believe I made or received any calls on this day.