Clear["Global`*"]
v = (F*Cos[th - t*w])/Zm - (A*B*Cos[phi + t*wd])/ E^(B*t) - (A*wd*Sin[phi + t*wd])/E^(B*t)

(*ÒÔÏÂÈ«ÊǸ³Öµ*) m = 0.5; F = 2; Rm = 1.4; s = 100; w0 = Sqrt[s/m]; B = Rm/(2*m); wd = Sqrt[w0^2 - B^2]; Xm = w*m - s/w; Zm = Sqrt[Rm^2 + (I*Xm)^2]; th = ArcTan[Xm/Rm]; phi = ArcTan[w/wd].(Rm/Xm); A = F/(Zm^2)*Sqrt[(Xm/w)^2 + (Rm/wd)^2]; t = 0; (*ÒÔÉÏÈ«ÊǸ³Öµ*)

Plot[v, {w, 0, 150}]

phi = ArcTan[w/wd]*(Rm/Xm);