My Outlook events are disappearing from my Phone. I'm still using BIOS 7.1.2. How do I fix this?

I have not upgraded to iOS8 (or 8.1 for that matter). I have an iPhone 5 with 40.2 GB available free space and a 7.1.2 iOS version.

The first time I noticed this issue was about 2 weeks ago. I got an event reminder and realized that I had entered the appointment at 12:45AM instead of PM. I opened the event on my phone and changed it to PM. It disappeared off of my phone. A few days later (when I remembered it), I checked my Outlook and the appointment was on my calendar (but still gone from my phone). I manually entered it again on my phone. It did not appear twice on my Outlook.

This week, I've noticed it again (similar but different). A co-worker traded weeks with me on a scheduled project. I had gone into my Outlook last week and changed all of the dates to the week of November 16th. THIS WEEK (when the items were originally scheduled), my phone has alerted me every day. I have been clicking "ok" and letting it go. I noticed this morning that clicking "ok" also deleted the event from my phone. I assumed it "disappeared" because the item was no longer listed for that day in my Outlook. I went to the rest of the week's appointments for that same task and changed the dates to the week of November 16. When I went to that week on my phone, there are no tasks listed.....GONE!

I've googled this issue and can't find anything recent.....there were items from 2009 and something in 2011 but nothing in 2014. I've checked my calendar settings in my phone and my work calendar (Outlook) is still checked to sync. Is anyone else having this issue? How can I fix it?