Aren't you supposed to be in 'sunny' california :)
Fake Suggestion: Downgrade to an iPhone 3G...I think they take less power
1. So I wonder if you have a bad panel in your 6 panel powerfilm, cause I would think at your latitude, that if I can charge in AZ with the same panel, you should be fine. You've probably already done this, but to check it. Clip a voltmeter onto the panel leads that go to the board (you can leave it connected to the board, just don't plug you're phone in. So you should get the green light. Measure the voltage to the board, it should be just under 20V! Then take a strategically cut piece of plane white paper, and cover just one of the 6 power film panels. You should see the voltage drop to the board, record that change for that panel. Remove the paper, see that the voltage goes back up, put the paper on the next panel, see that it goes back down about the same amount, and repeat. You might find that your total voltage out of the unloaded panels is low, and/or that covering one of your panels does not change the output voltage to the board by as much as other ones indicating a poorly performing panel or panels.
*****Most solar panels will drain energy from the system if they are damaged, so it's very important to know! With the same 5W powerfilm, my setup would NOT charge my iPhone 4S at .5A when any single one of the panels were covered! A bad or covered panel not only doesn't produce power, but sucks power, so it's a double hit.
2. The angle of the panel to the sun is VERY important. I'm sure you tried many placements, but I found in the canyon that 10AM to noon sun was the best even though I had to have the panel at a steep angle to catch the low sun.
*****The easiest way to gauge if your angle is right is to make sure that SHADOW it makes on the ground is a perfect rectangle or is is a trapezoid! I always held it up to see the shadow and get the angel in my head, I made sure the phone would charge at that ideal positioning, then I looked for a place to leave it in the same orientation for a while.
3. I haven't tried it, but I've heard of some guys using mylar or tinfoil wrapped cardboard to make a lightweight reflector to direct additional sun to the panel! If you try this, let us know how it works! It's probably not a permanent solution for you, but might give you some insight if the above stuff doesn't help.
Keep us posted!