On Itaku there's a drop-down box you have to click on to view NSFW or extreme NSFW, make sure you've found that and toggled it to display the birth content, otherwise it's invisible
There are five 2B items in the Itaku gallery: 3 static pictures, 2 animated PNGs. If you see those five items, you have seen everything in the gallery. If you're unable to see them, then I don't know what you're doing wrong because they're viewable with a normal account with NSFW enabled.
In fact, I just tested viewing the 2B pictures in a browser where I'm not even logged into Itaku, and once I enable the NSFW / Questionable tag, I can see the five 2B pieces. So you don't even need an account to see them.
Unless iPhone is blocking NSFW content, then I have no idea why you're unable to see content that is viewable even without an account. You must not be clicking the options I mentioned up above.