A well-ordered 25 ML epitaxial NiO(100) film on Ag(100) as prepared by layer-by-layer growth has been characterized by high-resolution electron energy loss spectroscopy. Six different phonon branches have been identified in the ΓX direction of the surface Brillouin zone and are compared with first-principles phonon calculations. Whereas the surface Rayleigh mode shows a strong upward dispersion of 173 cm⁻¹ in agreement with observations for the NiO(100) single crystal, the other surface phonons and surface resonances show only smaller dispersion widths in ΓX direction. The Wallis and the Lucas phonons are localized at 425 and 367 cm⁻¹ at the point, respectively. Additionally, two phonons are identified that have stronger weight at the zone boundary at 194 and 285 cm⁻¹ and that become surface resonances at the zone center. The dominant spectral feature is the Fuchs-Kliewer (FK) phonon polariton at 559 cm⁻¹, which is excited by dipole scattering and exhibits a rather broad non-Lorentzian lineshape. The lineshape is explained by a FK splitting resulting from the splitting of bulk optical phonons due to antiferromagnetic order. This view is supported by calculations of the surface-loss function from bulk reflectivity data.