iPhone/iPad sync Exchange calendar

I have an iPhone and an iPad - both use iOS 8.1.3 and both have Exchange on to sync my work calendar and emails.

Both also have a home calender on, and aol personal email.

Recently, my iPhone will not sync the exchange calendar, but my iPad does. Exchange appointments put in last year remain, but new ones made this year will not show in the phone if made in Exchange or show in exchange if made on the phone.

What is going wrong please? I've missed a couple of meetings, until I realised it is now not reliable. Thanks, Sarah