Hi everyone, I am totally new to Mathematica. I defined a function, Qi, in which only Phis and Vs are variables. I took the derivative of it based on Phis and call it Cs. Then I inversed VGFunc and I want to substitute it with Phis inside Cs formula and plot it based on VGFuncInverse; however, the plot is empty, could you please help me

q = 1.602*10^-19 (*coulombs*);
T = 300 (*Kelvin*);
NA = 10^16  (*1/cm^3*);
Ni = 10^10 (*1/cm^3*);
Ci = 0.00000345;
Vth = 0.026(*V*);
VFB = 0.7;
B = 1/Vth;
epsilonSi = 1.036*10^-12;  (*F/cm*)
LD = Sqrt[(epsilonSi*Vth )/(q*NA)]; 
CFB? epsilonSi/LD;
y = (CFB/Ci) * Sqrt[(2/B)];

Qi[CFB_, B_, Ni_, NA_, Phis_, 
  Vs_] := ((Sqrt[2]*CFB)*Ni*Exp[(B/2)*(Phis - Vs)])/(B*NA)
LogPlot[Evaluate@
  Table[Qi[CFB, B, Ni, NA, Phis, 
    Vs], {Vs, {0, 0.5, 1, 1.5, 2}}], {Phis, 0, 2}, 
 AxesLabel -> {"Phis", "Qi (log scale)"}, 
 PlotLegends -> {"Vs = 0", "Vs = 0.5", "Vs = 1", "Vs = 1.5", "Vs = 2"}]

Plot[Evaluate@
  Table[VGFunc[VFB, Phis, y, B, Ni, NA, Vs], {Vs, 
    Subdivide[0, 2, 5]}], {Phis, 0, 6},
 AxesLabel -> {"Phis", "VG"},
 PlotLegends -> (StringTemplate["Vs = ``"] /@ Subdivide[0, 2, 5])]

VGFunc[VFB_, Phis_, y_, B_, Ni_, NA_, Vs_] := 
 VFB + Phis + y*Sqrt[Phis + ((1/B) * (Ni/NA)^2 * Exp[B*(Phis - Vs)])]

VsValues = {0, 1, 2};
VGFuncInverse  = InverseFunction[VGFunc[VFB, #1, y, B, Ni, NA, 1] &]

Plot[VGFuncInverse[Phis], {Phis, 0, 5}, AxesLabel -> {"VG", "Phi_s"}]

Cs = D[Qi[CFB, B, Ni, NA, Phis, Vs], Phis]
CsFunc = Evaluate[Cs /. Phis -> VGFuncInverse[Phis]];
Plot[CsFunc[CFB, B, Ni, NA, Phis, 0], {Phis, 0, 5}]