Ok with this one you need to stay for the first fifteen, the trophies name is actually a bit of a joke because entamaphobia is the fear of doors. The way i did this is with a Gallo SA12 and aether shroud, tier 2. (I didnt finish upgrading it before this but tier 3 will make it easier). I recommend using attachments that increase salavage or equiment drop rate because it makes things easier. What i did was use the gallo to kill the zombies early on to get stuff like stun grenades and semetex and c4 using the salvage to buy it if necessary. When you get to around 6,7,8 your gun becomes a 2-shot to the body so you need to be more careful around then. If things get dicey and you get cornered use aether shroud and get out. Also train up the zombies and stun the before using lethals to kill the horde. The megaton will spawn on round 15 and he isnt hard if you buy a scorestreak, the combat bow if you were unlucky is an amazing choice and a chopper gunner helps more due to killing even more. By the way you wont get a dog round so be sure to not corner yourself if you gotta buy ammo from the crate. Id love to here any comments on what loadout you used by the way.