Not quite. Raven Guard can use their jump packs in both phases. Normally what will happen with a Jump Pack unit is that you can either choose to move as Jump Infantry and assault as Infantry, or move as Infantry and assault as Jump Infantry. The Raven Guard are allowed to move and assault as Jump Infantry.
You'd have to check out the unit type of Jump Infantry in the BRB to see what that means for both movement and assault. I'd give an exact page reference, but my rulebook is packed in my army case right now.