Calendars 5 is the best calendar, task-manager, and organizer for iPhone and iPad. Get it now if you haven't done so yet.
You can easily sync Calendars 5 with the iCloud calendar on your iPhone or iPad.
Now, the events from your iPhone or iPad calendar are displayed in Calendars 5.
To sync the calendars across your devices, make sure you're signed into the iCloud with the same Apple ID on both your iPhone and iPad.