During the flyby, DSN operators reported "a slight effect in the Doppler residuals," meaning that, as expected, Phobos' gravity had accelerated Mars Express' orbital velocity very slightly. Through careful analysis of the Doppler shifting of the radio signal, Phobos' gravity can be measured, allowing scientists to discern its mass and density - the most precise measurement to date.
All focus was on the spacecraft's ability to send a continuous stream of data back to Earth, so close-up snapshots were not a possibility.
ANALYSIS: Mars Express to Make Daredevil Flyby of Phobos
"In order to perform the Phobos flyby radio science measurements, the spacecraft needed to have its high gain antenna dish pointed at Earth for the entire duration of the flyby operations," said Scuka. "This meant that we were not able to conduct observations with any of the other instruments (which would need to be pointed at Mars)."
However, the operation allowed the spacecraft to beam back an extra 200 Gigabits of observational data, including imagery of Phobos during an earlier 500 kilometer pass of the moon.