<?php
$str='<li>Smartphone: Da</li>
<li>Touchscreen: Da</li>
<li>Tastatura QWERTY: Nu</li>
<li>Tip tastatura: Standard</li>
<li>Rezolutie senzor (Mp): 5</li>
<li>SAR (W/kg ): 1.17</li>';
print preg_replace('/<li\b[^>]*>\K[^<:]+(?=:)/i', '<strong>$0</strong>', $str);
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