This paper presents a smartphone based system for presenting light and sound stimulation to a user for neuromodulation experiments. A smartphone platform was used to increase ease of use and enable out-of-the-clinic experiments. The created Android app provides both visual and auditory entrainment stimuli, along with a real-time extraction of ongoing electroencephalogram (EEG) phase using a Phase Locked Loop (PLL) for enabling closed loop simulations. Both visual and auditory stimulation is provided accurately in the 1-20 Hz range using the smartphone class hardware. Test results for both gave R squared fit values of 1 between a fitted line and the measured stimulation frequencies. Data from 13 subjects showed the PLL could track EEG phase in the slow oscillation band with an error of 14.83±38.47°, with an average of 0.04±0.20 ms processing overhead per sample.