Trying to modify content.php

The answer is in your code. It’s even documented:

<?php if (is_search()) { // Only display Excerpts for Search ?> 
<div class="entry-summary">
    <?php the_excerpt(); ?> 
    <div class="clearfix"></div>
</div><!-- .entry-summary -->
<?php } else { ?> 
<div class="entry-content">
    <?php the_content(bootstrapBasicMoreLinkText()); ?> 
    <div class="clearfix"></div>
    <?php 
    /**
     * This wp_link_pages option adapt to use bootstrap pagination style.
     * The other part of this pager is in inc/template-tags.php function name bootstrapBasicLinkPagesLink() which is called by wp_link_pages_link filter.
     */
    wp_link_pages(array(
        'before' => '<div class="page-links">' . __('Pages:', 'wmillock') . ' <ul class="pagination">',
        'after'  => '</ul></div>',
        'separator' => ''
    ));
    ?> 
</div><!-- .entry-content -->
<?php } //endif; ?> 

There is clearly stated in the comment, that the if statement in the first line of code above is telling, that the excerpt should be shown only for search.

So what do you have to do? You have to modify the condition inside that if. How? It depends on what do you want to achieve…

If it should be shown on search and categories, you can use:

if (is_search() || is_category())

If it should be shown on every list of posts, then you can use negation of is_singular().

Here’s the full list of conditional tags.