Antiferromagnetic oxides offer a compelling paradigm for magnonics. Combining ab initio and spin Hamiltonian modeling, we map Cr2O3 from bulk to monolayer limits, verifying stability via phonon spectra. Contrary to previously predicted half-metallic ferromagnetic monolayer phases, we conclusively demonstrate that monolayer and bilayer configurations preserve an antiferromagnetic semiconductor ground state despite systematic gap narrowing. Intersecting magnon and phonon branches drive strong hybridization, establishing low-dimensional Cr2O3 as an ideal platform for quantum spintronics.