I agree with NGCHunter, in the TNG Technical Manual I think it says the apparent star-streaks are an artifact of warp-drive, NOT the stars wooshing past. It might be micrometeroids interracting with the warp fields for example.

Also, warp factors don't necessarily correspond to exact multiples of light speed, "depending on conditions in the sub-space domain and other factors". Perhaps warp 1 in the Pheonix was actually substantially less than light speed because of these effects.