Q: calendar synch

Probably a dumb question but cannot find it anywhere even though I cannot be the first.

I have two devices, an ipad air and iphone 5s, both recent new purchases both now on ios 8.13. All is well apart from the following which was the same on ios7 too.

The ipad calendar synchs with the iphone but not the other way. IOW I enter a new event on the pad and this appears on both pad & phone. However, if I create on the iphone it doesn't appear on the pad. I have checked all settings which appear the same. Any ideas please?

Thanks

Bill