(Checkbox array) reload form and values PHP

So i have a form and i want to NO clear fileds when form submitted.

I can this for simple inputs :

<input name="name" value="<?php echo $_POST['name']; ?>>

But i have array checkbox

<input type="checkbox"  name="ans[]" value="2" class="grp1" onclick="phaseCheck();">
<input type="checkbox"  name="ans[]" value="3" class="grp1" onclick="phaseCheck();">

how i can reload and check which checkboxes checked the user?

Thanks!