#1
can you plug the headphone out of a phone into the aux input of the peavey vypyr 2? I'm not sure of this is safe as it would be an amplified input.
#2
Sure, that's what it's for. Not a phone specifically, but any line-level device like a phone, ipod, CD player, etc.
#4
Not high enough to cause any damage. As I said, the aux input was specifically designed for what you're asking for. Most sound sources like an iPod or a phone aren't going to have a dedicated line out anyway, the headphone jack functions just fine as both. Just start with the volume low to avoid distortion or nasty volume surprises.