Problematic smartphone use (PSU) in adolescents—marked by compulsive checking, loss of control, and use despite negative consequences—can impair academic self-regulation. Guided by self-regulation and habit-formation models, this review synthesizes evidence linking PSU to reduced attention, lower self-control, procrastination, sleep disruption, and diminished academic achievement. Meta-analyses and longitudinal studies reveal small but consistent negative effects, moderated by age, trait self-control, mental health, family practices, and school environment. Evidence-based strategies include behavioural nudges, self-monitoring, mindfulness, physical activity, parental modelling, structured school policies, and app-based or clinical interventions. Multi-level, tailored approaches are recommended to protect learning while retaining digital benefits.