You create a spectral sword that hovers within range. It lasts for the duration.
When the sword appears, you make a melee spell attack against a target within 5 feet of the sword. On a hit, the target takes Force damage equal to 4d12 plus your spellcasting ability modifier.
On your later turns, you can take a Bonus Action to move the sword up to 30 feet to a spot you can see and repeat the attack against the same target or a different one.