We study the sensitivity of top polarization observables to the CP phase ζt in the top Yukawa coupling in the process pp→thj at the 14 TeV high-luminosity run of the Large Hadron Collider (HL-LHC). We calculate the top polarization in this process as well as an azimuthal asymmetry of the charged lepton arising from the decay of the top in the lab frame. We find that the dependence of this lab-frame azimuthal asymmetry on the phase ζt closely resembles the dependence of the top polarization on ζt. As compared to the cross section, which is sensitive to ζt for larger values, the lepton azimuthal asymmetry can provide a sensitive measurement of ζt for smaller values.