Did you know that Laravel has an undocumented validation rule?

As opposed to "starts_with" there is a "doesnt_start_with". Just add the translation key to validation.php and you are good to go.

'starts_with' => 'The :attribute must start with one of the following: :values.',
'doesnt_start_with' => 'The :attribute must not start with: :values.',

Example use

SomeInput::make('Swedish phone')
    ->rules([
        'starts_with:+46'
    ])
SomeInput::make('International phone')
    ->rules([
        'doesnt_start_with:+46'
    ])