I do basically agree with a single phase line between star systems, that seems to make more sense than between planets. A universe that makes no sense isn't fun.
I realize they add a strategic component to the game but I don't think it fits within the fictional universe very well. But, generally speaking, flying from planet to planet within a solar system makes sense. In space, you can fly in direct lines from point to point except to avoid storms or planets or stars or other phenomena.