Aim <p>Nomophobia, the fear of being without a mobile phone, significantly impacts mental health and sleep quality, particularly among Bangladeshi youth. Despite the increasing prevalence of smartphone dependency, its relationship with psychological well-being and insomnia has been underexplored.</p> Subject and methods <p>A cross-sectional online survey was conducted among 701 Bangladeshi youths (365 male, 336 female) aged 18–30 years. Nomophobia, psychological well-being, and insomnia were assessed via the Bengali Nomophobia Questionnaire (NMP-Q), the Warwick-Edinburgh Mental Wellbeing Scale (WEMWBS), and the Bangla Insomnia Severity Index (ISI), respectively. Statistical analyses included chi-square tests, ordinal regression, and multiple linear regression to identify associations and predictors.</p> Results <p>Significant relationships were found between the degree of nomophobia and mental well-being (χ² = 47.67, <i>p</i> &lt; 0.001) and insomnia (χ² = 107.42, <i>p</i> &lt; 0.001). Severe insomnia was reported by 81.82% of the participants with severe nomophobia. The predictors of nomophobia included socioeconomic status (<i>B</i> = 0.131, <i>p</i> = 0.018) and daily mobile use (<i>B</i> = 0.015, <i>p</i> = 0.049), whereas reduced sleep duration predicted insomnia severity (<i>B</i> = −0.128, <i>p</i> &lt; 0.001). Urban residents and men presented higher levels of nomophobia.</p> Conclusion <p>Nomophobia significantly affects psychological well-being and sleep among Bangladeshi youth, emphasizing the need for public health interventions. Strategies such as a reduction in smartphone usage, mental health education, and sleep hygiene promotion are recommended to mitigate its adverse effects.</p>