I have a similar issue. all earpieces, BT and wired, and speakerphone work fine. The phone's ear speaker goes virtually silent. you hear faint sounds if you listen carefully. I pulled the phone apart and looked at the speaker, made sure everything looked ok. nothing seemed wrong. Today I ran "alsamixer -c o" and kept it in the background and made a call and realized that the speaker actually works, I heard it clearly, but only under those circumstanced. Going to a backed up pre CSSU state didn't help.

This first happened to me after installing dbus-scripts to enable Bluetooth PAN tethering.