You can try this in your phtml file:

<script>
    require([
        'jquery',
        'jquery/ui'
    ], function($){
        $(document).ready(function(){
           $("#datepicker").datepicker({
           dateFormat: 'MM dd'
        });
     });
</script>  

Note: where "#datepicker" is the id of your datetime picker input element

You can try this in your phtml file:

<script>
    require([
        'jquery',
        'jquery/ui'
    ], function($){
        $(document).ready(function(){
           $("#datepicker").datepicker({
           dateFormat: 'MM dd'
           });
        });
    });
</script>  

Note: where "#datepicker" is the id of your datetime picker input element