Silicon photonic integrated circuits (PICs) show great potential for many applications. The phase tuning technique is indispensable and of great importance in silicon PICs. An optical phase shifter with balanced overall performance on power consumption, insertion loss, footprint, and modulation bandwidth is essential for harnessing large-scale integrated photonics. However, few proposed phase shifter schemes on various platforms have achieved a well-balanced performance. In this Letter, we experimentally demonstrate a thermo-optic phase shifter based on a densely distributed silicon spiral waveguide on a silicon-on-insulator platform. The phase shifter shows a well-balanced performance in all aspects. The electrical power consumption is as low as 3 mW to achieve a π phase shift, the optical insertion loss is 0.9 dB per phase shifter, the footprint is 67×28µm2 under a standard silicon photonics fabrication process without silicon air trench or undercut process, and the modulation bandwidth is measured to be 39 kHz.