Hi Mike. What are you measuring that gives you 0.87V? Is it PP_BATT_VCC? or PP_VCC_MAIN?
With a dead phone, you really have to start at the beginning. Check PP_BATT_VCC & PP_VCC_MAIN to see if they are shorted while the phone is unpowered. I wouldn't put any power on it until I am certain the main voltage rails are not shorted. If they are shorted, then that issue has to be resolved first.
If they are not shorted, then something downstream is causing the problem. I would then look at the output voltages of the PMU/PMIC (U7) to see if any of those are shorted. If there are shorts, then focus on those. Once all the shorts are gone, then power the phone to see what it does.