Hello, Marina_bixler.
We understand that Siri sometimes has a bit of a stutter in Apple Maps. We know how important clear and concise directions are and hope to help.
The first thing we recommend that you do is Restart your iPhone. This straightforward troubleshooting step is quick and often resolves any number of issues.
We also suggest making sure that the iPhone is backed up and up-to-date.
How to back up your iPhone, iPad, and iPod touch
Update your iPhone, iPad, or iPod touch
Do you connect your iPhone to your car system using Bluetooth or with a Lightning cable? If you connect wirelessly, is the issue still present when connected with a cable? If Siri is wholly disconnected from your car system and is speaking through the iPhone only, is the issue present?
If you change the voice of Siri, does that make a difference? Change Siri voice or language
If the issue isn’t resolved by an update or restart, please let us know the answer to these questions, and we'll go from there!
Be Well.