these days I was surprised that there is no out of the box solution to sync Microsoft Planner with Outlook calendar appointment. How this 2 services are part of Office 365 solution this can be connected and synced through Microsoft Flow.
When you successfully login to Microsoft Flow go to create new flow from the blank template. In connectors search for Planner. In this case I will create flow for sync new task into calendar.
In Plan ID I will choose my plan from planner.
Then click on New step and add action to Create event (V1).
In calendar ID choose calendar in which you want to see planner tasks, choose end time, start time, as mandatory fields.
At the end add flow name and save flow. Now when you create new task in planner it will automatically be sent to calendar.