HTML5 required attribute one of two fields

Question

I have a form with two required input fields:

Answer 1

For two text fields @Andy's answer is working awesome, but in case of more than two fields we can use something like this.

jQuery(function ($) {
    var $inputs = $('input[name=phone],input[name=mobile],input[name=email]');
    $inputs.on('input', function () {
        var total = $('input[name=phone]').val().length + $('input[name=mobile]').val().length + $('input[name=email]').val().length;
        $inputs.not(this).prop('required', !total);

    });
});