To get your Mac up and running again you can reinstall Mac OS via the internet recovery option. First, turn off the Mac, then hold in the 'Command' and 'R' keys at the same time. Don't let go, it may take a few minutes. It'll boot up to a white screen and will eventually show a globe. After seeing it you can let go. It'll then load up the recovery menu. Choose "re-install" Mac os and it will download and install the OS. Alternatively, you can create a bootable USB of your preferred Mac OS to install on your Macbook. Here's an article on how to do so on a Mac. https://support.apple.com/en-us/HT201372
Has the phone ever been repaired in that area? Maybe the charging port assembly was removed/replaced and wasn't installed correctly and the mic is being blocked. It also sounds like there could be dirt/dust in the mic hole which would cause it to not pickup sound or sound muffled.
So you're saying that you can only use loud speaker and not the earphone speaker at the top? The iPhone 6 has 3 different microphones, one on the bottom, one next to the camera on the screen and one next to the back camera.. I know siri uses the front mic. Try using siri and see if it understands you, also try taking a front facing video and see if you can hear anything back in the video.. If not then it sounds like whoever replaced the screen didn't install the front camera, prox sensor and mic flex cable or it may be damaged which would explain why sound recorder wouldn't work. It may also just be a software issue. Have you tried restoring it with iTunes?
Don't apply pressure to the screen because it might crack the display or LCD. It sounds like something may be stopping it from laying correctly in the phone. Try removing the display and make sure all the connectors are properly seated and that there isn't anything stopping the screen from laying down.