In this paper two GaAs samples were investigated; one was a very pure sample grown by chemical-vapor deposition, the other was grown by molecular-beam epitaxy. The dominant optical transition in the high-purity sample was the donor-bound-exciton transition. Phonon sidebands associated with both the free exciton and the donor-bound exciton were observed. The active phonons were the longitudinal-optical (LO) and the transverse-optical (TO) modes associated with both the free exciton and the donor-bound exciton at the Γ point in k space; the TO mode from the donor-bound exciton at the X point, the LO from the free exciton at the L point and/or X point, and the longitudinal-acoustical mode from the free exciton at the X point and the L point. These phonon-coupled exciton transitions were not observed in the sample grown by molecular-beam epitaxy; however, phonon sidebands associated with free-to-bound and bound-to-bound transitions were observed. The transverse-acoustical mode at the X point was observed along with lower-energy modes that were attributed to impurity and defect structures in the material.