IPhone 4S deleting contacts?

I've had two 4S iPhones for over a year now (first one fell and broke and I replaced it with a brand new one).

With each of these phones, about every month or so, it goes through a period where it will delete contacts entirely out of my phone book. Sometimes it'll compulsively delete only the most recently added 4-5 contacts, other times it just chooses randomly. If I don't have text messages from these people saved in my inbox, I lose their numbers entirely.

The OS doesn't seem to affect this issue - it's been consistent through 3 different software updates at this point.

No idea what to do! I have all my info backed up to iCloud, which backs up daily, but that also doesn't seem to make a difference in saving my contacts.

Any ideas?

Ha ha! Your contacts are running away from you! Lol! You may need an update of some sort. I do know my brother has one & i cant text him iPhone 4 has bugs he is pissed & getting a new one.why?me I have an LG Motion 4G lte its nice.