Final answer:
In a photo where Earth and the Moon are both fully illuminated, viewed from outer space, the moon phase visible from Earth would be a new moon, as the side of the Moon facing Earth would not be receiving sunlight.
Step-by-step explanation:
If an astronaut took a photo of Earth with both the planet and the Moon fully illuminated, as in the case of the Deep Space Climate Observatory spacecraft image, the moon phase visible from Earth at that time would be a new moon. This is because, during a new moon, the side of the Moon facing Earth is not lit by the Sun, which also means the far side of the Moon, the one facing away from Earth, is fully illuminated. Consequently, in the photograph where both Earth and the fully lit Moon are seen, the side of the Moon facing the astronauts (and the spacecraft's camera) is the one in full sunlight, while the side facing Earth is in darkness.