For purposes of battery behavior, I think it's the thermometer temperature, not the wind chill factor, that's likely to be important.
My guess is that attempting to charge the battery at low temps initially results in slow charge, but perhaps also warms the battery to a point where it eventually begins to accept a charge at a faster rate. The owner's manual potentially supports this idea, when it points out that "ambient temperature" can affect the time required to charge the PHEV. This might also be one of the important factors in reduced fuel economy that people have noticed in cold temps.
If this idea holds any water, then it raises some interesting questions for folks who live in cold climates. For one, is it smarter to begin charging the PHEV right after you get home, in the middle of the night, or at a time that will be reaching fully charged just shortly before you leave in the morning? If you begin charging right after you get home, presumably your battery is at a "happy" temperature where it can easily accept a charge. If you wait until the middle of the night, the battery will have cooled off by then and maybe you have to spend a few extra kWh on your electric meter with electricity that wound up going to heat the battery, rather than charging it (but depending on your electric utility, maybe those extra kWh are cheaper in the middle of the night). If you charge on a timer and charging doesn't begin until a few hours before you leave in the morning, by that time the battery might have cooled to ambient temp so you might be paying more kWh to charge, but perhaps there's a benefit in that if it was charging right up until the time you left, then the battery's already warmer than it otherwise would be, and that might mean that you get more benefit from regenerative braking in your morning drive than you would with a battery that was at ambient temperature.
For both HEV and PHEV owners, there might be a second thing to think about: if you drive the first mile or so in the morning in EV mode (without the ICE running, which means no heat and which I admit might be a stupid thing to do if you need a defroster, or if you have concerns that the ICE might not start due to the cold temps), then presumably the energy draw on the battery will help to warm up the battery and make it more receptive to receiving a charge from regenerative braking.
This is all speculation on my part, and I regret that I can't investigate it directly and report back on my findings. I used to live in a cold climate, but I don't at the moment. Instead, my personal concern is how to best take care of the battery when the temps in my area exceed 100 F (38 C) for weeks at a time (which they will surely do about six months from now). I'm pretty sure that in high temps, I should refrain from charging my PHEV to full charge, but I haven't found an easy way to do that. It would be nice if I could program the charging logic to stop at 80% instead of 100%.