I just resolved this on my LG G3. If you have your phone on silent and you try to go to speakerphone on a call, a glitch in the software keeps your phone mute. So the only way to prevent this is to take your phone off mute, and then make your call. I also disabled my voice enhancement too but I don't think that will make a difference.
I figured this out by unmuting my phone and making a voice call. When you put the speakerphone on and tap the volume button, it doesn't let you go all the way down to silent, however, when the phone is in silent and you make voice call, hitting the volume button on speakerphone doesn't adjust volume. LG needs to come up with an update/patch to fix this problem.
Hope that helps,
Toronto, Canada
I figured this out by unmuting my phone and making a voice call. When you put the speakerphone on and tap the volume button, it doesn't let you go all the way down to silent, however, when the phone is in silent and you make voice call, hitting the volume button on speakerphone doesn't adjust volume. LG needs to come up with an update/patch to fix this problem.
Hope that helps,
Toronto, Canada