The Onion

Completing the task with little effort in a disengaged fashion. In this case the task would be writing a satire article.

I've heard it for many decades in the acting world, usually when an actor isn't trying hard in a performance and merely reciting the lines to get to the end of the show.

The idea being you're not actually there doing the work (metaphorically), you're in bed at home phoning it in instead.

It means giving a bare minimum of effort. Like when there's an important meeting at work and you attend on the phone so you don't have to get dressed or go anywhere. The term came about back when phones were low quality but still convenient, so phoning it in was easy, but frustrating to everyone else.