To win in tennis, particularly in doubles, you have to assert yourself at the net. Many beginning and intermediate players shy away from the net because they don't want to get in the way of a fast-moving drive and possibly be struck.
One way to overcome such fear is to realize that you could catch with your hands almost any ball hit to you at the net. That realization alone should put you at ease, and trying it a few times in warmup sessions can convince you.
True, the ball arrives faster when you're at the net. But you don't have to move the racket as far to return it. Think of the volley as a short punch rather than a long stroke. Until you become accomplished, you simply can put your racket in front of a hard-hit ball and get it back.
Keep the racket up, watch the ball, and you have nothing to fear. On unusually fierce shots that come right at you, just block the ball back. Then as you gain confidence, try the pros' method of sliding the racket across in front of you from your backhand to your forehand side. That's how they handle the most fear some shot of all.