whenever I'm around my friend, or am talking on the phone with her, and I cast a spell, it always seems to work better than when I cast one on my own. Today, for example, I was talking to her on the phone because of bad weather. I decided to cast the "To Weaken a Storm" spell. I cast it while still on the phone with her and it worked better than it probably would have if I had cast it on my own. Am I unknowningly stealing my friend's energy? And if I am, is this a good or a bad thing?
It may be a possibility, but it's only a bad thing if it affects her negatively. If she feels tired or worn out after you cast the spell, she's feeling the effects of it. However, the damage is not permanent. A good meal and some rest is all she should need to start feeling better. If she takes care of her chakras and everything, then the damage would be repaired even faster.
Another possibility is simply that you feel more confident when talking to her. You already mentioned that you believe your spells work better when you talk to her than when you are not. That might be exactly why they do.