Distribution circuits with high penetrations of renewable energy resources may experience wide voltage deviations because of changing active power flows from distributed energy resources (DER). Traditionally these voltage swings have been mitigated with load tap changing transformers, capacitor banks, and other dedicated voltage regulation equipment. However, with the recent development of standardized DER grid-support functions, power electronics devices can also be used for voltage regulation operations. There has been extensive research regarding the proper employment of the autonomous volt-var function for voltage regulation, but a new centralized control technique based on extremum seeking control can find optimal reactive power settings for multiple inverters for a range of more complicated objective functions without the need of feeder models. This capability has been shown in power simulations and limited laboratory experiments using fixed power factor functions to adjust DER reactive power levels previously. In this work, we demonstrate the ability of extremum seeking control to provide distribution voltage regulation with multiple power hardware-in-the-loop (PHIL) distribution circuit simulations and a 3.0 kW photovoltaic inverter.