On the Contact record, if a contact has the value of 'CEO‘ in the Title...

The error condition formula of a validation rule should return TRUE when the validation rule should fire and display an error message. In this case, the validation rule should fire when the Title field has the value of ‘CEO’ and the Phone field is blank. The formula Title = ‘CEO’ && ISBLANK(Phone) returns TRUE when both conditions are met, and FALSE otherwise. References: https://help.salesforce.com/s/articleView?id=sf.fields_useful_field_validation_formulas.htm &type=5