Simple Answer, the port timing on the V3 Phantom in particular is less aggressive than it is on the Stihl saw it's based off of, and the Saw has no reeds. The reeds are a restriction to the intake, and if the intake charge volume going in is reduced greater by the reeds than the blow-back of the normal piston port design, there will be a loss in intake charge, and thus power.
As far as torque goes, In theory the Phantom should lose low end torque and power because a reed generally does increase power down low thanks to the higher crank case pressure generated by the reeds, BUT the design of most Saws - in particular the Stihl saws - is already meant to optimize low rpm torque due to how a Saw generally operates - being bogged down while cutting - which is why they try to optimize torque, and thus efficiency, in the low and middle RPM ranges.
With that said, it's only half a HP, and the reeds cut down on the blowback through the intake.
