I need help comforting my friend

Me and my best friend started getting into more serious topics and I’m not sure how to help him when he’s ranting, I know he doesn’t want advice just someone who will listen to him but I’m not sure how to make it seem like I’m here for them and idk how to comfort or cheer him up either- we talk over call so it makes it harder, I also go into a panic when he gets upset over something because of this so I could really use some advice.