If you watched the Earth, you would see it go through the same phases that the moon goes through. It would take the Earth 29.5 days to go through those phases, just as it does the moon, but the Earth's phases would be the opposite. When the moon appears to be full from Earth, the Earth would appear to be the equivalent of a new moon, a "new" Earth. When the moon was in its first quarter from Earth, the Earth would appear to be in its third quarter if viewed from the moon.
If you want to see how all of that works, try the Why is the Full Moon so Bright? activity.