You should calculate average coordinates.
You can do this on the 60CSx by:
* marking your location (mark button),
* give it a name you can remember
* Go to Find -> Waypoints -> Your waypoint
* Press Menu -> calculate average (not sure, mine is in dutch)
It will start to do measurements (you will see a counter of how many) of your location. I usually take 15-20 before I fix it. The more you do, the more accurate it gets.
With lots of foilage, I'd go for 40-60
I wouldn't use the iPhone to mark a location, especially if you have such a fine device already ^^