You can use a basic csv file with column header of PhoneNumber and just drop in numbers underneath. There is no formatting of the phone numbers required, you do not need to add +1, remove dashes or parenthesis. Outside of the PhoneNumber, our system has default attributes for Email, FirstName and LastName. If you wish to include these column headers and drop in info. If you do not require this information, they do not need to be included in file. If you wish to create additional attributes for storing data, simply include as additional column headers and system will give you the opportunity to ignore column, create new attribute (in which you will be required to select data type) or map to existing attribute via drop down.