The PhD will form part of a broader interdisciplinary research programme in mobile health and AI, with applications in areas such as mental well-being, fall prevention, stroke rehabilitation, and chronic disease prevention. The PhD student will work in an interdisciplinary team spanning behavioural scientists, clinical psychologists, computer scientists, AI engineers, and health systems researchers. The position involves close collaboration with research partners in Singapore, including Nanyang Technological University, National University of Singapore, Tan Tock Seng Hospital (TTSH) and Duke-NUS Medical School, as well as public health and healthcare stakeholders. The PhD student will be responsible for designing, developing, and validating a comprehensive agentic AI platform that supports multimodal data ingestion, knowledge retrieval, and LLM-based workflows for the delivery of evidence-based coaching strategies, including motivational interviewing. This includes analysing time-series data from smartphone sensors and usage logs using advanced statistical and machine learning approaches to develop personalised nudging and adaptive interventions. The candidate will also lead the development of a cross-platform mobile application for delivering and monitoring these interventions, including deployment and management of the associated backend infrastructure. The PhD student will work in close partnership with researchers developing hardware interfaces for device data ingestion and will support clinical validation studies to evaluate the feasibility, acceptability, and effectiveness of the developed interventions with end-users and key stakeholders. The candidate will also contribute to ethics submissions, data governance documentation, and analysis plans in accordance with Singaporean and international research standards. The role involves publishing findings in high-impact peer-reviewed journals and presenting at leading international conferences. Given the applied, translational nature of the project, the position offers exceptional opportunities for professional development and for contributing to healthcare innovations with direct real-world impact across domains including mental well-being, stroke rehabilitation, falls prevention, and chronic disease management.