Q: I can't hear on voice calls and they can't hear me but they can on FaceTime

Hi, Eddie.  

Thank you for visiting Apple Support Communities.  

I understand that your iPhone may be experiencing issues with the receiver and possibly the microphone.  Here are a couple articles that I would recommend going through for these issues.  If none of these steps help this issues, please see the section labeled Get more help.  

If you can't hear a person on a call or voicemail or if the sound quality is poor on iPhone

If your voice is too faint or sounds unclear using iPhone, or iPod touch

Cheers, 

Jason H.