According to G3.5's website sure. Most people I've read from who've tried both to any extent agree that Phoenix has much better heli physics and somewhat better airplane physics as well. G3.5 has a bunch more features than Phoenix, but in the flight physics area I think it loses.

Disclaimer: I've spent a lot of time using Phoenix, but only maybe an hour or two on G3.5, but I feel that the helis definitely feel more real in Phoenix.