Processes for producing polyethylene terephthalate copolyesters are disclosed, that include the steps of: esterifying a mixture of at least terephthalic acid, from 20 mole percent to 45 mole percent 1,4-cyclohexanedimethanol, and ethylene glycol, optionally in the presence of one or more alkaline earth metals or alkali metals, to form an oligomer; polycondensing the oligomer in the melt phase in the presence of aluminum and one or more alkaline earth metals or alkali metals, to obtain a copolyester having an intrinsic viscosity of at least 0.5 dL/g; and thereafter adding to the copolyester a phosphorus-containing compound.