To subscribe to the calendar or download the actual content in isc format:
To view the calendar in a browser (Just as a backup solution in case the ordinary calendar is down, – no color coding)
Guidelines for subscribing:
See for example the guide Import or subscribe to a calendar in Outlook on the web on Microsoft Office support site.
With Google Calendar open, on the left hand side under other calendars, select Add a new calendar and then Add from URL and paste in the address above to create a new calendar with a subscription from the Planner
You can find numerous guidelines by searching the web for How to subscribe to calendars on iPhone and iPad