This umbrella review of 34 meta-analyses, representing 235 randomised controlled trials done across 52 countries and 48 957 participants and ten chronic conditions, aimed to evaluate evidence on the efficacy of mobile phone interventions for populations with chronic diseases. We evaluated the strengths of evidence via the Fusar-Poli and Radua methodology. Compared with usual care, mobile apps had convincing effects on glycated haemoglobin reduction among adults with type 2 diabetes (d=0·44). Highly suggestive effects were found for both text messages and apps on various outcomes, including medication adherence (among patients with HIV in sub-Saharan Africa and people with cardiovascular disease), glucose management in type 2 diabetes, and blood pressure reduction in hypertension. Many effects (42%) were non-significant. Various gaps were identified, such as a scarcity of reporting on moderators and publication bias by meta-analyses, little research in low-income and lower-middle-income countries, and little reporting on adverse events.