What makes you think it’s short…even a phone that is powered off still draws some current for the “always on” part of the circuit and potentially to charge the battery.
The proper way to test for shorts is to measure with a multimeter with the battery disconnected. Check the BATT_VCC, VCC_MAIN and PP5V0_USB lines to see if they are shorted. You can use Ohms mode or check with the DMM in Diode mode. If those lines are good, then start checking the PMIC outputs. Only when you’re satisfied the phone has no major shorts do you put power on it, otherwise you can damage the board further.
Report back with your findings and we can give you more guidance.