She was talking to you on her cell phone and almost got into a wreck because she was messing with the phone. She's rattled because of the whole ordeal.
Man Truth ... She should not have been messing with the phone while driving. She should have paid more attention. As usual, you should keep this (thought it may be true) to yourself. She's probably perfectly aware of it anyway.
When reacting to her telling you of this scenario, here are some things not to do...
In fact, if you take any of these courses of action, you will lose ground in your husband-goal of acheiving relational closeness with your wife. She will be less likely to come to you in the future with such concerns. She is your partner, part of you... not your student.
You need to express compassion and understanding. Even if what she did was really stupid. She is making herself vulnerable to you; do not be harsh and crush her with a typical male response. You need to tend to her feelings here, not the situation or facts. This is an aspect of your role as her protector.
By being tender and compassionate, you will convey to her that you are a safe place where she can come during life's "storms". And that is precisely one of the goals of being a good husband.
One key is not to talk much. Let her do the talking. Let her express herself to you without fear. She's looking for a shoulder to cry on... emotional support. And that, above all else, is what you need to provide.
You've blown it in the past? Many have. It will take work to gain her trust back, but keep working on it... carefully. And don't force anything. Consider the ParableOfTheSunAndWind. It will also take skill on your part to master the balance between treating her tenderly (like a lamb), but not putting her beneath you (like a child).