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',
]);
$("input.phone").inputmask("+7 (999) 999-9999");