Validation Gravity form
add_filter( 'gform_field_validation', 'validate_phone', 10, 4 );
function validate_phone( $result, $value, $form, $field ) {
$pattern = "/^(\+44\s?7\d{3}|\(?07\d{3}\)|\(?01\d{3}\)?)\s?\d{3}\s?\d{3}$/";
if ( $field->type == 'phone' && $field->phoneFormat != 'standard' && ! preg_match( $pattern, $value ) ) {
$result['is_valid'] = false;
$result['message'] = 'Please enter a valid phone number';
}
return $result;
}