Speaker Phone Mic Echo

Hi, I replaced the screen on my girlfriend's iPhone 6, this is my first attempt ever repairing a phone, so it was pretty stressful. I completed it, mostly successfully. Everything works, except for the speaker phone. I called myself from that iPhone to test out all the mic's, and when I enabled speaker phone, it gives back this really echoey feedback. What could I have done wrong inside the phone and how would I fix that?