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The Phone field lets people enter a phone number, validated for U.S. or international format.

The Phone field type supports the following Field Settings:

You can choose between the following formatting options:

U.S. Format—displays three separate textboxes. Respondents must enter 10 digits total. Only accepts numerical digits.

Sample of the US format phone field type.

International—displays one textbox. Only accepts numerical digits, but there's no limit on how many digits someone can enter.

Sample of the international phone field type.

There's no extension setting, but you can add a Number field immediately after the Phone field and use CSS Layout Keywords to place them side by side.