Mental health (MH) has become a global issue with increased numbers, especially after COVID-19. Digital phenotyping in mental healthcare provides a highly effective, scaled, cost-effective approach to handling global MH problems. We propose a conceptual design of an MH monitoring application for both patients and clinicians. The application is designed to monitor the overall MH status of individuals based on mood, stress, behaviour, and personality. Further, it proposes objective MH assessment from smartphone data and screening of MH via periodic, short, self-reported, standardized questionnaires. This solution yields customized explainable MH assessments for individual users and clinicians to build user trust and system credibility.