To ensure safe operation of the power grid, distributed power sources connected to the grid need to have islanding detection capabilities. Traditional over/under frequency (OUF) and over/under voltage (OUV) methods for islanding detection have a significant non-detection zone (NDZ) when applied to islands formed by virtual synchronous generator (VSG)-controlled inverters and grid-following inverters. To address this issue, the expressions for voltage amplitude and frequency are first derived for the scenario where grid-forming and grid-following inverters jointly form an island. Based on this, it is verified that the OUF and OUV methods cannot accurately detect the islanding condition. Then, a method for islanding detection is proposed by calculating the rate of change of voltage phase in the dq frame. Additionally, angular frequency error negative feedback is introduced into the active power loop of the VSG to improve detection accuracy and sensitivity. Finally, an islanding model of grid-forming and grid-following inverters using PSCAD is built, and the simulation validates the effectiveness of the proposed method.