It is possible to determine key parameters of a cosmic ray air shower from different approaches. One of the most important elements of an air shower is the place where the shower axis hits the ground, the shower core. Determining the position of this component can result in calculating other important characteristics of a cosmic ray. In this study and based on CORSIKA and COREAS simulations we present a new approach to show the possibility of finding the position of this point by analyzing the slope of the phase angle from radio signals. The simulations were performed for different type of air showers with 0.1 to 1 EeV energy with Proton and Iron as primary particles. In order to consider the effect of the geomagnetic field as the most important mechanism in creation and propagation of radio signals from cosmic ray air showers, we choose two different locations in the South and North hemispheres namely Pierre Auger Observatory and the location of the expected Semnan Radio Array. The result shows a direct relation between the slope of the phase angle and the distance from shower core. We investigate the relation of this parameter to the initial energy, the shower arrival direction and the geomagnetic field value. In all conditions, we calculated the radio signals at the shower core to have on average, the minimum slope as a function of frequency using a specific computer code developed for this study.