The US space agency's new robotic craft on Mars has been commanded to carry out a second practice dig before beginning its real work.
Controllers want another test run to perfect their technique before Phoenix begins excavating Martian soil for scientific purposes.
When the arm collected and released its first scoopful of soil on Sunday, some of the sample stuck to the scoop.
Phoenix touched down successfully on Mars' northern plains on 25 May (GMT).
"The team felt they weren't really comfortable yet with the digging and dumping process," said the mission's chief scientist, Peter Smith, from the University of Arizona, Tucson.
"They haven't really mastered it."
The extra practice means the earliest that Phoenix would flex its 2.25m-long robotic arm to claw below the planet's northern plains for scientific study would be Wednesday.
Professor Smith likened Phoenix's efforts to a child playing on the beach with a sand pail and shovel.
"But we're doing it blind from 170 million miles away," he said.
Phoenix has already taken a scoop of Martian soil
Phoenix landed near the Martian north pole, which is thought to hold large stores of water-ice just below the surface.
It will carry out a three-month mission to study Mars' geological history and determine whether the Martian environment could once have supported life.
Images taken by the robotic arm camera revealed the spacecraft may have uncovered patches of water-ice when its thrusters blew away loose soil during the landing.
Phoenix got its first touch of Martian soil on Sunday when it scooped up and then dumped a handful of soil in a region dubbed the "Knave of Hearts".
The scoop contained intriguing white specks that could be surface ice or salt.
For the second practice "dig and dump", engineers told the robot to go slightly deeper in the same region and use the camera on its arm to take photos this time.
Doors to one of the ovens failed to open properly
Phoenix has its own laboratory on board. Any dirt and ice it scoops up will be shovelled into several small ovens to be heated.
The resulting gases will be analysed by a variety of scientific instruments.
New photos sent back by Phoenix showed one of the spring-loaded doors on the oven complex had failed to open all the way.
Scientists hope Mars' midday temperatures will make the door less sticky, but it can still be used with a partially open oven door, said Professor Smith.