You can start a new recording straight from your lock screen with Tape It:

record from lock screen.mp4

It's the fastest way to record audio on your phone.

To add Tape It's record button to your lock screen, touch and hold on your lock screen, then choose Customize. Tap below the time to choose widgets to add, and tap on Tape It.

Have a look at Apple’s documentation on how to add widgets to the lock screen if you need more detailed steps.