A measurement of the $Bs0\to J/\psi \varphi$ decay parameters using 80.5 $\mathrm{fb}-1$ of integrated luminosity collected with the ATLAS detector from 13 TeV proton-proton collisions at the LHC is presented. The measured parameters include the $CP$-violating phase $\varphi s$, the width difference $\Delta \Gamma s$ between the $Bs0$ meson mass eigenstates and the average decay width $\Gamma s$. The values measured for the physical parameters are combined with those from 19.2 $\mathrm{fb}-1$ of 7 TeV and 8 TeV data, leading to the following: \begin{eqnarray*} \phi_s & = & -0.087\phantom{0} \pm 0.036\phantom{0} ~\mathrm{(stat.)} \pm 0.021\phantom{0} ~\mathrm{(syst.)~rad} \ \Delta\Gamma_{s} & = & \phantom{-}0.0657 \pm 0.0043 ~\mathrm{(stat.)} \pm 0.0037 ~\mathrm{(syst.)~ps}^{-1} \ \Gamma_{s} & = & \phantom{-}0.6703 \pm 0.0014 ~\mathrm{(stat.)} \pm 0.0018 ~\mathrm{(syst.)~ps}^{-1} \ \end{eqnarray*} Results for $\varphi s$ and $\Delta \Gamma s$ are also presented as 68% confidence level contours in the $\varphi s$-$\Delta \Gamma s$ plane. Furthermore, the transversity amplitudes and corresponding strong phases are measured. $\varphi s$ and $\Delta \Gamma s$ measurements are in agreement with the Standard Model predictions.