From Birnam Designs Wiki

You can modify the MaxRows value, which is the page limit when displaying results. This is normally 30, i.e. for more than 30 results the results are split into pages.

Edit /usr/share/phpmyadmin/config.inc.php (or wherever this is located on your system) and modify or add this line:

$cfg['MaxRows'] = 300;

With '300' changed to whatever value you would like.