It looks like you're having some problems with your iPhone ringing for incoming calls even though you have Do Not Disturbed enabled. I certainly understand the importance of having Do Not Disturb working correctly when you need it to. I'm happy for the opportunity to help you with this!
First, let’s make sure your settings are in order in Settings > Do Not Disturb. If your iPhone is ringing only for certain contacts but not for others, select Allow Calls From and adjust it accordingly. If some of your calls are silenced but calls from the same caller aren't, check to see if you have Repeated Calls enabled. With this feature enabled, the second call from the same person won't be silenced if that second call is placed within 3 minutes. You'll also want to check to see if you have Scheduled enabled in your Do Not Disturb settings. If you do, calls and notifications will only be silenced during the selected time frames. You can view more about Do Not Disturb settings here:
Use Do Not Disturb on your iPhone, iPad, and iPod touch
If you still experience problems after adjusting your settings, reply back answering the following questions:
- Which iOS version are you using on your iPhone? View the version in Settings > General > About.
- Is the problem actually with the Do Not Disturb while driving feature?
- Do you experience this issue only with specific contacts and/or certain times of the day?
- Do you also get audible alerts for other types of notifications when Do Not Disturb is enabled?