The CP-violating weak phase φ_s and the decay width difference ΔΓ_s between the light and heavy B⁰_s mass eigenstates are measured with the CMS detector at the LHC in a sample of 48 500 reconstructed B⁰_s → J/ψ φ (1020) → μ⁺ μ⁻ K⁺ K⁻ events. The measurement is based on a data sample corresponding to an integrated luminosity of 96.4 fb⁻¹, collected in proton-proton collisions at √s = 13 TeV in 2017–2018. To extract the values of φ_s and ΔΓ_s, a time-dependent and flavor-tagged angular analysis of the μ⁺ μ⁻ K⁺ K⁻ final state is performed. The analysis employs a dedicated tagging trigger and a novel opposite-side muon flavor tagger based on machine learning techniques. The measurement yields φ_s = −11 ±50 (stat)±10 (syst)mradand ΔΓ_s = 0.114 ±0.014 (stat)±0.007 (syst)ps⁻¹, in agreement with the standard model predictions. When combined with the previous CMS measurement at √s = 8 TeV, the following values are obtained: φ_s = − 21 ±44 (stat)±10 (syst)mrad, ΔΓ_s = 0.1032 ± 0.0095 (stat)±0.0048 (syst)ps⁻¹, a significant improvement over the 8 TeV result.