antonkabaev

print $form->field($model, 'phone')->label(false)->widget(\yii\widgets\MaskedInput::className(), [
	'mask' => '+7 (999) 999 99 99',
])->textInput(['placeholder' => $model->getAttributeLabel('phone')]);

// ну или коротко..
print $form->field($model, 'phone')->widget(\yii\widgets\MaskedInput::className(), [
	'mask' => '+7 (999) 999 99 99',
]);