During its third day on the Red Planet, the lander moved its arm, said Matthew Robinson of NASA's Jet Propulsion Laboratory in Pasadena, Calif.
"We're pleased that we successfully unstowed the robotic arm," he said in an announcement. "In fact, this is the first time we have moved the arm in about a year."
NASA said the Phoenix was instructed to rotate its "wrist," unlatch its launch lock, raise the forearm, and move it upright to release the elbow restraint.
NASA planned to test the arm at various temperatures, then command the arm to reach under the spacecraft with a camera to provide a view of the terrain and the bottom of the lander itself.
Soon, the robotic arm will dig into the soil and deliver samples to lab instruments for analysis. The information is likely to give clues about whether life is, or has been, possible on the planet.
"We are now making plans for where to dig first and what we'll save for later," Phoenix principal investigator Peter Smith, of the University of Arizona, said in a statement.
The mission also announced that it had successfully activated a laser instrument that detects dust, clouds, and fog. The lidar, provided by the Canadian Space Agency, sends out rapid pulses of green laser-like light into the atmosphere. The light bounces off particles and reflects back to a telescope.
"The Canadians are walking on moonbeams," said Jim Whiteway, a Canadian scientist from York University, Toronto. "It's a huge achievement for us."
Whiteway likened the task of delivering the lidar -- while maintaining alignment within 1/100 of a degree -- to aiming a baseball "from home plate to the center field wall, holding that aim steady after launch for a year in space, then landing."