I have a code to plot the steady state frequency response curve (provided by @ Michael E2), How can I plot the steady state phase response with the help of this code same as shown in the figure:
\[Kappa]=1.4;
WE = 0.2;
\[Omega] = Sqrt[3*\[Kappa]*(1 + WE) - WE];
f = 0.2;
\[Epsilon] = 0.2;
amp[w_, w0_?NumericQ, damping_?NumericQ] /; w == 0 = 1.;
amp[w_?NumericQ, w0_?NumericQ, damping_?NumericQ] :=
Block[{x}, #[#["Domain"][[1, -1]]] &[
x /. First@
NDSolve[{x''[
T] == (1/[Epsilon])((((1 +
WE)(1 + [Epsilon]x[T])^(-3[Kappa] -
1))) - ((1 + [Epsilon]*
x[T])^-1) - (WE(1 + [Epsilon]x[T])^-2) - (4*
damping[Epsilon]^2(x'[
T])(1 + ([Epsilon]
x[T]))^-2) - ((3[Epsilon]^2(x'[
T]^2)(1 + [Epsilon]x[T])^-1)/2) - [Epsilon]^3*
fSin[T (w0 + [Epsilon]^2 w)]), x[0] == 1, x'[0] == 0,
WhenEvent[x'[T] < 0 && T > 5000, "StopIntegration"]},
x, {T, 0, 5010}]]];
Off[NDSolve::ndsz]
pltNum = Plot[
Evaluate[Table[
amp[w, [Omega], z], {z, {[Epsilon]*0.04}}]], {w, -5, 5},
PlotStyle -> {Thick, Dashed, Red},
PlotLegends -> Placed[{"Numerical"}, {0.8, 0.8}], PlotRange -> All]
Any help would be highly appreciated. Thanks!

