A retarding field energy analyzer (RFEA) is used to measure the time-averaged ion energy distributions (IEDs) on thesubstrate in both continuous wave (CW) and synchronous pulse modulated radio-frequency (RF) inductively coupled Arplasmas (ICPs). The effects of the phase shift q between the RF bias voltage and the RF source on the IED is investigatedunder various discharge conditions. It is found that as q increases from 0 to p, the IED moves towards the low-energyside, and its energy width becomes narrower. In order to figure out the physical mechanism, the voltage waveforms onthe substrate are also measured. The results show that as q increases from 0 to p, the amplitude of the voltage waveformdecreases and, meanwhile, the average sheath potential decreases as well. Specifically, the potential drop in the sheath onthe substrate exhibits a maximum value at the same phase (i.e., q = 0) and a minimum value at the opposite phase (i.e.,q =p). Therefore, when ions traverse across the sheath region above the substrate, they obtain less energies at lower sheathpotential drop, leading to lower ion energy. Besides, as q increases from p to 2p, the IEDs and their energy widths changereversely.