The gain‐loss laser oscillation condition is applied to photoexcitation geometries in which phonon‐assisted laser operation is observed in AlGaAs‐GaAs quantum well heterostructures (QWHs). The model is found to agree with a variety of experimental conditions in which cavity size, photoexcitation spot size, and mirror reflectivity are varied. Also, it serves to indicate further how others might have failed to observe phonon‐assisted laser operation in QWHs and how photoexcitation geometries can be varied to verify these results.