We're looking to roll out Microsoft Teams Phone System to one of our education clients, which is of course going to increase their adoption of Microsoft Teams in general even further. As they also use Moodle, I am equally keen to test out the new integration.
While I don't have a definitive answer to your question as to whether or not the Moodle instance needs to be deployed with SSL for the integration to work or not as it isn't specified above, knowing how Microsoft are with Security I would suggest this is a likely yes.
Even if that wasn't a prerequisite, I'm not sure why you would want to deploy a Moodle instance even for testing without SSL. Especially if it has API integration with any areas of a production Office 365 tenant.