This is not supposed to be, how do you defend an uppercut in general. This is supposed to be how to defend against an uppercut specifically as an infighter/swarmer. While staying on the inside. Without getting out of range, only staying on the inside
There are a couple of different ways. First, get your lead shoulder into his chest, if you are fighting out of an angled stance. That takes one hand out of the game entirely and you can see the other hand. Second, pay attention to where you put your head. If you have your head on his left shoulder, the only uppercut he can hit you with is with his right hand and you can keep your left arm in the way of that. If your head is on his right shoulder you only have to watch his left uppercut.
You can also catch uppercuts like you’re wearing mitts. Keep your hands tight to your chin, and when you catch the uppercut, just give a small downward tap with your glove—don’t overreact. If he notices you’re dropping too far, he’ll feint and hit you with a hook.