Recent developments in growing highly n-doped wide bandgap oxides such as β-gallium oxide (β  −  Ga₂O₃) and more recently zinc gallate (ZnGa₂O₄) have opened avenues toward important applications, such as transparent electrodes and ohmic contacts. Magnetoconductivity measurements provide a unique method to assess the contribution of phonons to mobility over a wide range of temperatures. For β  −  Ga₂O₃ and ZnGa₂O₄, initial attempts to interpret the measured magnetoconductivity raised fundamental questions about the interplay between the large number of phonon modes in these lattices, electron–phonon scattering, and lattice disorder. Here, we use density functional theory modeling of electron–phonon scattering to help rationalize magnetoconductivity measurements for a wide range of electron concentrations n and temperatures in β  −  Ga₂O₃ and ZnGa₂O₄. The results provide a first-principles understanding of dominant low-field mobility features suggested by phenomenological models used traditionally for semiconductors with high lattice symmetry.