I have an 5C. Why do I hear only half my calls.

I have an iphone 5C. I only hear my phone ring, texts, half of the time. It will show up that I have missed my call. Since I am not switching setting in between, what would be the cause of this? My daughter will call, get voicemail, leave a message, then call right back. I will then hear the phone ring. I have missed several important calls by not hearing a ring. HELP!!