The "Phone Number" node collects the user’s phone number. The difference between Phone Number and a regular free text node is that the user's response is validated for a correct phone number format.
In some cases, such as collecting an extension, the validation may cause a false negative error. If this is the case, you can optionally choose to disable the phone number validation which would allow the user to enter any phone number format. The user's reply to a Phone Number node will automatically be saved as the Phone Number user property.