What does turn off/on airplane mode do?

All of sudden I couldn’t make or receive any phone calls. All in- or out-coming calls lasted for a ew seconds and went straight to “failed”.

The bot suggested to turn off and then on airplane mode. I tried and it indeed fixed. What did this action do? I’ve never had such experience with T-Mobile.

PS: don’t test 911 when trouble shooting calling. Although my call to 911 went through, I couldn’t pick up the call-back (a regular phone number) from police station. It failed and hanged up automatically 3 times in a row. I was so stupid.