Most of a Jedi's combat ability comes from their ability to be in tune with the force and "see" into the future. It's likely that using all your concentration to control your "phantom blade" would cause you to lose your combat sense, not be effective, tire easily, AND defenseless. Basically, it's more effective, easier, and safer to actually wade into battle than to stand on the sidelines and attack with your saber.
---Jedi Guardian of the Newbie Questions
---Masters of the Force Team Leader / Creator
---Open Jedi Project Lead Moderator / Co-Founder