We describe a novel camera phone-based optical sensing platform capable of real-time quantitative fluorescence-based measurements. The platform employs the phone's camera as a photodetector in a non-imaging optical configuration that simultaneously detects fluorescence from a number of sensor spots on a disposable optical sensor chip. The platform combines the functionality of the camera with the phone's data-processing capabilities to facilitate on-phone analysis of detected fluorescence intensity. It is envisaged that such a platform will have significant potential in application areas such as environmental monitoring and healthcare where there is a growing demand for decentralized diagnostics using low-cost, portable devices, particularly in remote or low-resource environments.