Phe is, in fact, excreted from the body in people with PKU. The newborn screening test is based on that, in that it is a urine test. PKUers excrete a higher amount of phe in urine than non-PKUers, which is how a first screening for PKU is done. Non-PKUers do not excrete as much phe because their bodies break down the phe correctly, so there is less available to be excreted. As to how long it takes the body to excrete phe, I don’t know the answer to that.