When the boss moves around you can follow the propeller for a small amount of points. Following the propeller is most lucrative during the aimed blue shots. During the purple side spreads it's most lucrative to absorb the spreads at an angle to gain some graze, while also absorbing the bullets with your aura.
When the boss is about to stop, which is generally after 4-6 movements, for either blue or purple pattern:
You should prepare to line up with the propeller to get a graze off of the buzzsaws that will be deployed from both side of the propeller. This is best done with Speed 3 so you can assume position to shoot the buzzsaws with your laser without sacrificing any shots upon them. This is imperative as the tic points from shooting the buzzsaws are the most lucrative aspect of Phase 1 scoring.
The buzzsaw graze, when done properly, is worth about 4000pts per cycle. It is a substancial moment of graze score one can go for. It will keep you busy during phase 1 scoring, which is otherwise a fairly boring phase. In this example I am not doing it perfectly; gaining about 2000-3000pts per cycle.