In a Microsoft Dynamics CRM 2011 organization, the Phone Number field on the account entity has a requirement level of Business Required.
What are the potential sources of records that have a missing phone number?
Users might have deleted the phone number when saving accounts.
Users might have used CRM for Outlook to synchronize the CRM account records with Outlook account records that do not have a phone number.
A user might have imported account records with no phone number by using the Data Import Wizard.
The enterprise resource planning system, which creates accounts in CRM through a one-way integration by using the CRM web service, might have created accounts with no phone number.
Users may have ignored the warning about the missing phone number when saving new account records.