A measurement of the B0s → J/ψφ decay parameters using 80.5 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 φs, the width differences between the B0s meson mass eigenstates and the average decay width s. The values measured for the physical parameters are combined with those from 19.2 fb −1 of 7 and 8 TeV data, leading to the following: φs = − 0.087 ± 0.036 (stat.) ± 0.021 (syst.) rads = 0.0657 ± 0.0043 (stat.) ± 0.0037 (syst.) ps−1s = 0.6703 ± 0.0014 (stat.) ± 0.0018 (syst.) ps−1

Results for φs and s are also presented as 68% confidence level contours in the φs–s plane. Furthermore the transversity amplitudes and corresponding strong phases are measured. φs and s measurements are in agreement with the Standard Model predictions.