I pretty much agree with honk here.
A good Free Race sail with 2 cams, or a good free race camless sail like a Sailworks Retro, Severne NCX in the 8.5 m2 size range would be ideal for the Phantom 320 with a
75 Kg. sailor.
Cambers do not add any appreciable power to a sail, they just make it more stable in higher winds.
The large free race camless sails mentioned above have the same power and in some cases better low end power than fully cambered race sails the same size.
Hope this helps,