It's possible to get yourself stuck after being saved by the pit upgrade. Well after my stamina ran out I was still humming along on the bottom of the screen, passing under gates and avoiding villagers quite unharmed.
Phantogod can be beaten without the bug. Key is to have all your party leveled at least with their main stat for the HP. You want full runes especially health, damage and health regen. Your goal while fighting the boss should be to stick to him as much as possible, thinning down groups with your ult whenever they get clustered. Your other goal is to collect as many ghosts as possible. Your allies do solid DPS to the boss if they are allowed to do so unhindered.