Why does a country code appear in the Phone field even when left blank?

This happens because the Phone Country Code setting in your preferences is set to a specific country. To prevent the country code from being auto-filled, change the setting to Local in your My Preferences page.
Follow these steps to not show the country code in the phone field:

1. Log in to the CRM. 
2. Click Main Menu.
3. Select My Preference. The My Preference page opens. 
4. Click Edit. 
5. Go to Phone Country Code.
6. Select Local. 
7. Click Save.