Smartphone-based healthcare and diagnostic biosensors are adaptable, cost-effective, and accessible alternatives to traditional medical devices. This study examined smartphone-integrated biosensor advances in illness diagnosis, health monitoring, and personalized medicine. Biosensors on cell phones enable portable, real-time health examinations for a broad population by leveraging mobile technologies. How the electrochemical, optical, and biosensing biosensors detected biomarkers for diabetes, cardiovascular disease, infections, and cancer was also considered. This review focuses on user-friendly smartphone apps and mobile health (mHealth) platforms for data collection, processing, and interpretation. This study observed that even though smartphone-based biosensor technology has advanced, there are unresolved challenges. Addressing biosensor sensitivity and accuracy issues is crucial to reliable diagnostics. The effects of human variability, environmental disturbances, and sensor calibration on performance require improved sensor accuracy. Production costs, scaling problems, and healthcare system interactions slowed adoption in resource-limited regions. This study shows the need for affordable, easy-to-use sensors that can give patients and doctors vital information. Smartphone biosensors will benefit from nanotechnology, AI, and ML. These improvements should be smartphone biosensors' usability, precision, and efficiency, making them more reliable and versatile for consumer and medical use. Smartphone-based biosensors may improve individualized therapy, preventive care, and healthcare delivery, according to studies. This review also presents information on smartphone-based biosensor technology's advances, problems, and future uses.