The default Phone number and Mobile phone number fields only accept numbers and the following characters that are commonly found in phone numbers: + - ( ) . x. You can further validate phone numbers in form submissions by restricting the length of the number a visitor is able to enter. You can also allow visitors to select their country from a dropdown menu to include a country code in their phone number.
Please note: phone number settings must be set on a form-by-form basis.
In your HubSpot account, navigate to Marketing > Lead Capture > Forms.