The robotic arm on Phoenix reached out and touched something.  It left an impression of its scoop in Mars’ soil that looked very much like a footprint.  The arm seems to be in good working order.  And here’s the picture if you don’t want to click on the link to NASA’s website.

As you can see, the impression left by the scoop actually does look like a footprint.  The first footprint on Mars, made by a scoop.