At time t = 0 and at position x = 0 m along a string, a traveling sinusoidal wave with an angular frequency of 440 rad/s has displacement y = +4.5 mm and transverse velocity u = – 0.75 m/s. If the wave has the general form y(x, t) = ym sin(kx – ωt + Ф), what is phase constant Ф?