Once a recording is running you are free to do something else with the phone. Junior says as much while it records: "Recording will continue if you leave".
Lock the phone or switch apps and recording continues. A live indicator stays on your lock screen and in the Dynamic Island, showing that Junior is recording and how long for. You can pause, resume and stop from there without unlocking. See quicker ways to record.
If the app is closed by the system while recording, Junior recovers the audio the next time you open it and takes you to the details form so you can save it.
Check the timer when you come back
Whatever interrupted you (an incoming call, a low-battery warning, the system reclaiming memory), the check is the same: look at the elapsed time and compare it against how long you have been talking. If they disagree, end the recording and start a fresh one rather than carrying on.
Questions
Will it keep recording in my pocket?
Yes. Neither locking the phone nor putting it away stops a running recording, and the screen turning off makes no difference. What does stop it is force-closing Junior from the app switcher, or the phone running out of storage or battery.
What happens if someone calls me mid-recording?
The phone call wins and Junior's recording is interrupted for its duration. It picks up again by itself afterwards. The catch is that the elapsed timer keeps running throughout, so the number on screen can end up ahead of the audio that was captured. Check it when you return.
I swiped Junior away by accident while recording.
On an iPhone, reopen Junior. It finds the recording, recovers what was captured, and takes you to the details form to save it. On Android there is no automatic recovery, so check the upload queue for a recording left on the device, and contact support if it is not there.