On any iPhone, when choosing a select, the design moves to Bootstrap, why?

Question

iPhone

On any iPhone, when choosing a select, the design shrinks
on all other devices, this does not happen.
What can be a jam and how to fix it?
bootstrap is used

here is the layout

<div class="well col-sm-12">

    <?php $form = ActiveForm::begin(
        ['id' => 'digital-calc-form'],
        ['enableClientValidation' => true],
        ['enableAjaxValidation' => true],
        ['validateOnChange' => true]
    );
    ?>
    <div class="row">
        <div class="col-sm-6">
            <?= $form->field($model, 'paper', [
                'template' => '{label}<div class="input-group"><span class="input-group-addon"><i class="fa fa-file-o fa-fw" aria-hidden="true"></i></span>{input}</div>{error}'
            ])->dropDownList(ArrayHelper::map(
                Digital::find()->orderBy(['position' => SORT_DESC])->all(),
                'id',
                'title'
            ), ['onchange' => 'getData()']) ?>

Answer 1

If you are confused by the fact that you have a standard iPhone select window (by the way, it is also the same on windows phone), then you can read this: ru.stackoverflow.com/questions/229360/%D0%9A%D0%B0...