You don't need a three second exposure with a modern camera and a fast lens. F/1.2 or f/1.4 with low-light stacking at 1/10 to 1/2 will more than do it for moonlight.
Plus, it has artifical light, a phone screen, so even less than that would be useful.
As for AF, the obvious solution is to simply have a light in the camera. Mine does, it works fine even in complete darkness. I've actually gone and took a photo of a subject lit only with a phone screen, in perfect darkness, at around 2 meters.
Result? F2.8, 1/10x3 (stacking), ISO6400 actual, ISO2066 effective.
Very, very far from a challenging situation. Actually, quite easy.
With my F/1.4 lens, a cellphone screen provides enough light to illuminate a wooden plank to a shutter speed of 1/25 at ISO4000. More than serviceable. Especially with stabilization, where I can in reality get away with 1/2.
You know, dedicated cameras also evolved. A lot.
At the issue of this expriment, I can be confident that my camera can take pictures of much higher quality in the same conditions, at a higher resultion with much less noise and more detail, and all that at half of the price. Indeed, an a6000+EF-speedbooster+Tamron28-75 2.8 EF will run you 600$ tax included, for a higher performance, and will last you a decade or more.
EDIT: for some reason, I can't answer since I'm rate limited, but I can actually do a 3 second exposure, hand held, with my camera, and get a sharper result that that. Especially if I'm tipsy. Here's how I do it - I put my camera in image stacking mode, set the shutter speed to 0.8 seconds, and fire the shutter.
My camera will then take 4 pictures with IS on for 0.8 seconds in each of them, recenter IS in the few milliseconds between them, then warp and shift the images together and stack them. Bam, 3(.2) second exposure. It's not always the sharpest on the first try, but it's a hell of a lot sharper than whatever is in the picture there. Also, the iPhone is rejecting quite a few images there, so it won't be 3 seconds and more like 1.2 seconds.
Especially at the wide focal lengths equivalent to an iPhone. It's not very hard. I was at 1/20 before to ensure maximum sharpness, but if I'm willing to either stack in post or take 2-3 shots, more than possible.