Call parking in Teams is very useful if you want to swap devices you've taken a call on or if you want to park a call for someone else until they become available to take that call.
To place a call on hold on one device and pick it up from another device, also known as parking a call, click More actions 
in your call window and select Call park 
.
After you park the call, Teams will give you a unique code you can use to retrieve the call. If someone else is retrieving the call, copy the code and share it with them.
To retrieve a parked call, go to the speed dial tab, click Unpark , and enter the park code.
Retrieving a parked call on a mobile phone (Teams App) or a Teams-enabled Deskphone follows a similar concept.
On a mobile, open the Teams App and press the Call + button:
Then click the Call Park button:
This will bring up a dialogue for you to enter the parked call code you receive from the place you parked your call.
If no one picks up a parked call within 5 minutes, it’ll ring again.
Note: If you don't see any options for call parking in your settings, talk to your IT Admin.