Flashing apple logo, phone won't turn on

Alright, so I recently got a temporary phone as I wait for my actual one to come in. The temp. one is the iPhone 6. I've had it for about 3 days. Today, it randomly turned off and I could've sworn that it was at least at 30%. I didn't think much of it and plugged it in. Then, the phone randomly began turning on and off. It would turn on - taking about a minute - then turn off again about 5 minutes later. Each time it would turn on it would only be at 1 or 2 percent and wouldn't charge any more. Then it started taking longer to turn back on again. This time, the percent would switch from 100 to 1 each time it would turn on. Now, it won't even turn on. The apple logo keeps flashing on the screen. This only happens when it's plugged in, though. When it isn't plugged in I can't get a response from it at all. Any ideas?