Mobile phone usage among young adults in Nairobi slums has seen significant growth but disparities exist based on gender. A mixed-methods study combining quantitative survey data (N=300) and qualitative interviews (n=20) to explore gender-specific patterns of mobile phone use and communication practices among youth aged 18-25 in Nairobi slums. Gender disparities were observed, with women using mobile phones less frequently than men, particularly for financial transactions. Qualitative data revealed that women's reluctance stemmed from concerns about privacy and security issues related to their gender identity. The study highlights the need for targeted interventions addressing these specific socio-technical challenges faced by female youth in Nairobi slums. Public health campaigns should focus on enhancing mobile phone security features while also promoting digital literacy programmes that address privacy concerns and economic empowerment through mobile applications.