how to show all category's name for select product

[akhtar]

hi
how to show all category's name in select product, in product details page
example:
category's name: Mobile, Samsung, Samsung mobile, Samsung Phone

product select above mention all category

i am use

<?php echo $product->category_name;?>

but this code showing only 1 category, please help me how to show all category name in product details page:

joomla : 3.8.3
VirtueMart 3.2.12
joomla default template
using PHP 5.5.12