The optical spectrometer is a widely established and widely used scientific instrument for analyzing biochemical samples. However, it is expensive, bulky, and requires an external power source and a computer to operate, which makes it difficult to use in resourcelimited countries and in remote locations. Advancement in smartphone technology has led to the development of portable, low-cost smartphone-based spectrometers. However, the lack of smartphonebased software and automatic wavelength calibration results in irrelevant workloads for students within the time limit of the course. In addition, most smartphone spectrometers are only able to capture images. As a result, a computer becomes an essential tool for the student to process and analyze the sample spectrum. Unlike many other smartphone-based spectrometers, our developed device also provides a smartphone application for both Android and iOS platforms. Thus, measurement data and data plots are transferrable among smartphones and computers. In addition, the wavelength calibration is carried out automatically using an embedded reference white light LED by the application. Furthermore, the provided 3D-printed parts, part lists, and circuit board are included with an example of an iPhone 7 mount, as well as their assembly instructions. Our developed device features a sufficiently quantitative measurement for wavelength ranges from 411.2 to 700 nm. For the spectral resolution, our device achieved resolutions of 9.8, 13.4, and 21.7 nm at wavelengths of 405, 532, and 650 nm, respectively, when evaluated with an iPhone 7.