In-coating phenyl phosphonic acid (H₂PP) additions are studied to assess their effect on corrosion-driven organic coating disbondment inhibition from a hot-dip galvanized (HDG) steel surface. In-situ scanning Kelvin probe experiments carried out on HDG samples, coated with model polymer organic films containing H₂PP at various levels, showed a delay of up to 20 h. The rate of delamination was shown to decrease by up to 94% when compared with a control coating. The observed delamination kinetics suggest an inhibitory mechanism whereby H₂PP additions form a cathode-blocking salt layer with the zinc substrate. The possible effects of H₂PP, HPP^- or PP^2- leaching and a buffering of the highly alkaline rendered underfilm pH are also discussed. It is shown that, with increasing levels of in-coating H₂PP, the time for delamination kinetics to become established is increased and the delamination rate is substantially decreased.