If telephone number contains 9 digits -
It will be Saved as it is in Salesforce - Ex: 949243871
If telephone number contains 10 digit -
It will be Saved as : (895) 623-1245
If telephone number contains 11 digits there are 2 cases
· If 11 digit number starts with 1 it will automatically convert in the 10 digit format by removing the 1 in the number
Ex: If the number is like this => 12365478963
It will be saved as in Salesforce => (236) 547-8963
Note: It removes the 1 and formats the other numbers as like 10 Digit Number.
If 11 digits but not starting with the 1 then it will stored as it is in the Salesforce.
Ex: If the number is like this => 23654789631
It will be saved as in Salesforce => 23654789631
If you do not want this formatting for a ten- or eleven-digit number, enter a “+” before the number, for example, +49 1234 56 78-0.
Note: A phone field can accept a maximum of 40 digits to be entered in the field. Also note that this can only be done via User Interface and NOT via the API.
For your reference, here are the articles related to your issue:
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