Calendars 5 uses Google Calendar as a server for uploading and downloading new events. Therefore you can sync events from iPad to iPhone and vice versa through your Google Calendar.
Note: you need to use same Google account on both devices.
Calendars 5 syncs data automatically to and from your Google account at startup and every time you create a new event.
Note: Events Calendars 5 gets from iOS calendar (Local Calendars) will not sync with Google calendar.