A search for charge-parity (CP) violation in Cabibbo-suppressed D+s→K0Sπ+, D+→K0SK+, and D+→ϕπ+ decays is reported using proton-proton collision data, corresponding to an integrated luminosity of 3.8  fb−1, collected at a center-of-mass energy of 13 TeV with the LHCb detector. High-yield samples of kinematically and topologically similar Cabibbo-favored D+(s) decays are analyzed to subtract nuisance asymmetries due to production and detection effects, including those induced by CP violation in the neutral kaon system. The results are ACP(D+s→K0Sπ+)=(1.3±1.9±0.5)×10−3,ACP(D+→K0SK+)=(−0.09±0.65±0.48)×10−3,ACP(D+→ϕπ+)=(0.05±0.42±0.29)×10−3,where the first uncertainties are statistical and the second systematic. They are the most precise measurements of these quantities to date, and are consistent with CP symmetry. A combination with previous LHCb measurements, based on data collected at 7 and 8 TeV, is also reported.