Chris, your easiest method is to first find true Sth using Solar noon and a plumbob. This bypasses any magnetic deviation errors or misreading the compass etc.
Then your iPhone can download a free app (or cheap) for a Declinometer.
Set your mount up reasonably level with the polar axis pointing south as per your marked out site. Place the iPhone with it's app on the mount body and adjust the angle to equal your latitude. That should plce it pretty close to aligned.
After that guiding takes over to correct any minor drift that occurs if you have a guide scope\computer setup.
See below pic of my EQ6 on the driveway. The wooden bar at the far side is aligned E/W and also levels my driveways slight slope southwards. There are some little yellow paint marks on the driveway beneath the wooden bar and the rear ( Northernmost ) foot of the tripod.
Using this setup I have been able to just place the bar and drop the tripod on and been ready to go within 10 minutes or so. Without guiding I have been able to get 2-3 minute exposures with almost undetectable drift.
Takes a bit patience I know but once you figure out what the object of the exercise is it gets a lot easier.
