Another way to add the calendar. If the above does not work on your phone (e.g. you have multiple google calendars/IDs) then you can add this calendar to your phone by explicitly adding this calendar: https://calendar.google.com/calendar/u/0?cid=Y184bW5jOG4zazN0cXByN2dua29iaXI3cGh2NEBncm91cC5jYWxlbmRhci5nb29nbGUuY29t