ListPlot[Table[{n,EulerPhi[n]/n},{n,10000}],AxesOrigin->{0,0}]

ListPlot[Table[{n,If [PrimeQ[n+1],EulerPhi[n]/n,0]},{n,10000}]]

ListPlot[Table[{n,If [PrimeQ[n+1] && EulerPhi[n]/n<0.18,1,0]},{n,100000}]]

Sum[If [PrimeQ[n],EulerPhi[n-1]/(n-1),0],{n,2,200000}]/PrimePi[200000]+0.0