It would be great if there would be power apps trigger that would start the power apps flow when user receive a call on teams.
We think over integrating telephony with teams and we want to pop up CRM page with client data when the call is received by sales person. That would allow us to easily implement such a solution.

Alternative way would be allowing the flow to be manually triggered on the ongoing conversation like it is already available for messages in the selected message trigger (https://docs.microsoft.com/en-us/connectors/teams/#for-a-selected-message). That is less automated but still would do the job for us.

Such trigger should pass the call id into the flow so additional information (participants) could be read using teams graph api.