Linked from
The 12 pages that link to Phenylalanine, each with the reason it gives.
TyrosineRelated: Phenylalanine is tyrosine's metabolic precursor and a close structural relative.
EpinephrineRelated: Its metabolic pathway supplies the starting material for epinephrine synthesis.
CoumarinRelated: Plants can channel it into the precursors used to make coumarin.
Cinnamic acidRelated: Plants can form cinnamic acid by removing ammonia from phenylalanine.