may be in this way, example for Phone in item-post.php
instead of :
<label for="phone"><?php _e('Mobile Phone', 'veronika'); ?></label>
use:
<label for="phone"><?php _e('Mobile Phone', 'veronika'); ?>
<?php if(strpos($required_fields, 'phone') !== false) { ?>
<span class="req">*</span>
<?php } ?>
</label>
$required_fields has to be declared early and inserted above the form.
<?php $required_fields = strtolower(osc_get_preference('post_required', 'veronika_theme')); ?>