It comes down to duration and consumption.
As a financial planner and investment manager I am responsible for my clients' entire life savings and absolutely cannot have comms go down. I'm never 100% unplugged or "on vacation". Yep, it sucks sometimes but it's just part of the gig. So, lugging the extra weight is a necessity. I have a smaller Goal Zero and it's okay if I know I'll only need to charge my phone and battery pack a couple times during a period of good weather forecasts, but the much larger Ankers (sp?) I have are the cat's meow for longer duration trips in inclement weather. I've used them to trickle charge batteries on overcast days. Just be mindful of needing to set them up and monitor them so they are aimed directly at the sun.
If you're only going to be out for a couple days, you're phone will probably be fine if you are vigilante about minimizing power consumption and protect it from the cold. Things that don't do well in the cold get to enjoy some space in your sleeping bag at night and under a layer or two of of clothing during the day.
If you're only going to be out for 3-6 days, then bringing along a battery pack is the way to go, with the same caveats of protecting if from the cold. I've had great luck with the Dark Energy Poseidons and larger Ankers (sp?).
If you're going in on the 12th and coming out the 26th and you have a significant need for regular battery consumption...then a battery pack with an accompanying solar panel is the way to go. More of each if your base camp is supported by four-legged beasts of burden and you spike out for a couple three days at a stretch before coming back to base camp for food, fresh base layers, fresh batteries, etc. A couple extra power cords are a good idea. Two is one. One is none. I had to relearn that the hard way when a power cord decided that it no longer wanted to participate in charging my phone from a battery.