Hi , I just bought your Apple iPhone 8 plus yesterday and I am getting a problem in ear speaker when I am calling someone the call voice quality is very bad and volume is very low please tell me how I can clear this problem

See these support documents.

If you can't hear a person on a call or voicemail or if the sound isn't clear on your iPhone - Apple Support

If you hear no sound or distorted sound from your iPhone, iPad, or iPod touch speaker - Apple Support

I was struggling with my iPhone 8 microphone for several weeks trying everything suggested on this forum and others. I tried everything from changing voice haptics to network resetting plus a handful of other suggestions. Here is what so easily fixed my issue and I'm hoping will help others. If you are an AT&T customer shut off your LTE setting. Says it might slow your connection but who cares if you can't actually talk to the person without having microphone/speaker issues.

1. Open the Settings app on iPhone and choose “Cellular” at the top of the list
2. Tap “Cellular Data Options” (in newest versions of iOS, older do not have the sub menu)
3. Tap on “Enable LTE” and choose “OFF” (or alternatively, you can set ‘Data Only’ to stabilize some voice calls, or “Voice & Data” as the default)*
4. Wait a moment for the iPhone cellular connection to cycle on and off again and 3G / 4G should now be on as default with LTE off, as visible in the status bar of the iPhone

My husband had same issue with his iPhone 8 and from what I can recall I had the exact issue with my iPhone 6 until an AT&T rep recommended I try to shut off the LTE (I had unfortunately forgotten this when I purchased my 8)

Hope you find or have found the answer to your issue.

Did you upgrade to the latest OS , or check for any updates of the OS?