I noticed my phone having shorter battery life and staying warm when I wasn't using it.
In Settings > Privacy > Location Services I disallowed the Facebook app from being able to use my location.
Problem seems to be solved. My iphone now stays at room temperature when I'm not using it.
How did I decide to turn off location services for Facebook?
iOS 7 added a feature allowing apps to occasionally update in the background. For example, if you always check Facebook when you wake up, wouldn't it be cool if Facebook updated itself just BEFORE you woke up and was therefore ready for you with current data? Then you wouldn't have to wait.
When I went into the location services settings, I observed Facebook had a solid purple arrowhead which indicates Facebook had recently used my location. However, I knew I hadn't touched the Facebook app all day.