Hi,
Please check the points mentioned here for troubleshooting echo
http://www.cisco.com/c/en/us/support/docs/voice/voice-quality/19640-echo-ipphone-gateway.html
http://www.cisco.com/c/en/us/support/docs/voice/voice-quality/40309-show-call-act-voice.html#topic6
For general voice quality issues you can check the following
https://supportforums.cisco.com/document/101961/how-troubleshoot-voice-quality-issues-ucm-environment-bad-sound-dead-air-one-way
HTH
Manish