Background: Smartphone addiction is becoming increasingly prevalent among adolescents and young adults and has been linked to various physical and psychosocial conditions. However, its association with gastrointestinal functional disorders such as functional dyspepsia (FD) and irritable bowel syndrome (IBS) remains understudied, especially in Pakistani populations. Objective: To determine the association between smartphone addiction and the prevalence of FD and IBS among individuals aged 12–35 years. Methods: A cross-sectional study was conducted among 350 young adults aged 12–35 years for the period of one year (March2025 to Februray2026). Smartphone addiction was assessed using the Smartphone Addiction Scale-Short Version (SAS-SV). FD and IBS were diagnosed using Rome IV criteria. Data were analyzed using descriptive statistics, Chi-square tests, and Odds Ratios with significance set at p < 0.05. Results: Of 350 participants, 289 (82.6%) met the predefined criteria for smartphone addiction. FD was present in 217 (62.0%) and IBS in 229 (65.4%). Smartphone addiction was significantly associated with FD (Pearson χ² = 51.91; p < 0.001; OR = 8.86, 95% CI: 4.32-18.17) and IBS (Pearson χ² = 68.38; p < 0.001; OR = 12.30, 95% CI: 5.98-25.30). Conclusion: Smartphone addiction was significantly associated with functional dyspepsia and irritable bowel syndrome in this sample. However, the cross-sectional design precludes causal inference. Further prospective studies are warranted to clarify the direction and mechanisms of these associations.