We propose and implement a simple and compact quantum random number generation (QRNG) scheme based on the quantum phase fluctuations of a DFB laser. The distribution probability of the experimentally measured data fits well with the simulation result, got from the theoretical model we established. Min-entropy estimation and Toeplitz-hashing randomness extractor are used to obtain the final random bit. The proposed approach has advantages not only in simple structure but also in high random bit generation rate. As a result, 502 Gbits/s random bits generation speed can be obtained, which is much higher than previous similar schemes. This approach offers a possibility to promote the practical application of QRNG.