In the calendar below, click on “iCal/RSS button” or 

In your phone Settings:

Settings > Accounts & Passwords > Add Account > Other > Add Subscribed Calendar > Where it says “Server” add this iCal link: https://www.calendarwiz.com/CalendarWiz_iCal.php?crd=opepta  > Next > Save

If you don’t see the above options available, you can add the iCal feed via:
Settings > Mail, Contacts, Calendars > Add Account > Other > Add Subscribed Calendar > Where it says “Server” add the iCal link > Next > Save

Please note that the iCal link is CASE SENSITIVE and must be exact and with no spaces.