The 'Incoming Call' node is where your flow begins. Whenever a phone call is received on the provided phone number, your flow will be triggered.
The phone number. Must support flows.
Note that each number can only be linked to one flow. If you attempt to create a second flow using the same number, you will get a warning telling you it is already linked. If you publish the second flow, your first flow will be unlinked.
Every call flow begins with an 'Incoming Call' trigger. See any example: