Most of the ONTs themselves are actually extremely small, its the absolutely ridiculous plastic housing they put them in that takes up a bunch of room, granted this is for excess fiber storage so it does need to have some extra space to curl up the extra cable. Luckily I've observed some of their newer units are slimmer than their older units.
How many floors up is your apartment? If its on the 1st or 2nd story, you should be able to request a outoor ONT. This is a box that would be mounted outside your residence, and then the only box inside your house would be your router.
Otherwise, you will have to get an indoor unit, but you should be able to deny the battery backup which takes up more space (Its quite useless anyway, unless you have phone service). Without the battery backup, the units pertrude out of the wall by a few inches, and are about 1.5 feet by 1.5 feet long. They are a plain black box with a Verizon logo on it, and should be fairly easy to hide. I would take a photo of a newer install I've witnessed but I'll have to come back to post it.
