While previous PKU intervention research has largely focused on pharmacological treatment of elevated Phe levels, the adaptation of evidence-based psychosocial therapy holds promise for addressing cognitive and psychological symptoms and significantly improving quality of life. Study goals include: (1) to demonstrate the efficacy and feasibility of a short-term skills-based intervention (Show Me FIRST) for anxiety and depression in adolescents with PKU, and (2) to further establish the psychometric validity of novel assessment measures recently developed by the Investigators that utilize ecological momentary assessment (EMA) to capture in the moment neurocognitive and psychological function. The Investigators propose to conduct a randomized controlled trial wherein 30 adolescents with PKU will be randomized to either an immediate intervention group or wait-list/delayed intervention group.