The betting money is on DrGeoff's diagnosis, that the unit was fried by an external voltage. But if you're in to chasing down and eliminating any other possibiities...
Your Phone2 port's readings look remarkably like a hard short. Are you sure there's nothing in that rj11 socket? Maybe a hair-width strand of copper wire? Give it a careful looking over with a very bright flashlight and reading glasses. And maybe a toothpick to probe between the wires, fish out any hair, dust bunnies, etc.
Has the unit been seriously dropped or banged? Not just bumped, but like knocked across the room or onto a stone floor? If the jack is externally clean, it's either an electronic failure straight up, or a very slight possibly of an electrical problem caused by breakage or debris inside the unit, causing a short.