Basically this. I've been camping out in the wilderness for years in parts where it's legal (deep into the Jefferson national forest area) and the like, and I've been through some pretty bad storms out there. Freezing rain is a lot to deal with, though, and the amount of time you'll spend under shelter just passing it by almost defeats the point of being out in the forest. And that's just in Virginia.
Phil would probably deal poorly with temperature and weather, but honestly shit like ticks is what I think would get him. I'm not sure how it is on the west coast, but raccoons, ticks, and "minor" hazards tend to be the biggest problems in my experience. The odds you'll even see a bear are pretty low, is especially if you do what you're supposed to and make a lot of noise (I think Phil's massive girth and stumbling could do this accidentally, really.) That said, you're probably right. He'd get spooked the second he realized he couldn't see the way back out of the woods, and either just sloth it there in misery until he figured it out and bullshit some story about how he traveled too deep into the terrifying Black Forest of Brothers Grim fair, or with any luck run off in a random direction, get more lost, and die tripping over a rock and breaking his legs falling into a ravine or something.
Of course, he's breaking the first safety rule anyway and going out alone with no reliable means of sending for help. He really may as well be a potato at that point.