no caller ID on a second incoming call on IPhone 6

If i'm talking to someone, and someone else tries calling in, I get a beep notification of this second call, but NO caller ID. sometimes I dont even get an option to swtich over to the second call. I either have to let it keep beeping , or hang up on original caller. Why is this?

Also, if i am (albeit once in awhile), able to switch over to the incoming call, I am UNABLE to switch back to the original call. Sometimes a "swap" message appears, but almost all the time I end up hanging up on everyone. so i have been ignoring any second calls when I'm engaged in conversation. this is a $600.00 phone that is seemingly able to do everything except what the phone was originally invented for. anyone have a fix?