With the release of IOS 12 it was discovered that by using Siri, you could bypass the lock screen.  Unfortunately, the  latest security update does not fix that problem.  To ensure that your phone stays secure, change your settings to disable Siri when the screen is locked.

To change your settings:

1. Open settings.
2. Select Siri & search.
3. Scroll down to find Allow Siri When Locked.
4. Click to disable it.