Grandstream Reception Phone Call Quality Fix

I'm experiencing intermittent poor call quality on my Grandstream reception phone. This issue occurs randomly throughout the day, not limited to peak hours or specific calls. Occasionally, there are error messages when trying to receive calls, but not consistently.

Ideal Skills and Experience:
- Proficiency with Grandstream phone systems
- Experience with diagnosing and fixing call quality issues
- Knowledge in troubleshooting network-related problems
- Capable of interpreting error messages and understanding their implications
- Good communication skills for explaining technical issues in simple terms.

Please provide a detailed plan on how you intend to resolve these issues.