By default there is no quantity form field for add to cart button in category/items view. Phoca Cart uses layouts like Joomla and therefore it is possible to edit button layout in custom layout (stored in template).

Copy this file:

components/com_phocacart/layouts/form_part_start_add_to_cart_list.php

to your template:

templates/your_template/html/layouts/com_phocacart/form_part_start_add_to_cart_list.php

and change from:

echo '<input type="hidden" name="quantity" value="1">';

to:

echo '<div class="input-group bootstrap-touchspin"><input class="form-control ph-input-quantity" type="text" name="quantity" value="1"></div>';

This code not only displays the quantity form field, but also adds plus and minus buttons if the Quantity Input Spinner parameter is enabled in Phoca Cart options.

Phoca Cart - Quantity form field in category/items viewPhoca Cart - Quantity form field in category/items view