- strpos: documentation ( source)
<?php
$event = ['categories' => 'meeting;skype'];
$needle = 'meeting';
$haystack = $event['categories'];
if( ($pos = strpos( $haystack, $needle )) === false){
echo "\n$needle not found in $haystack";
}
else
{
echo "\n$needle exists at position $pos in $haystack";
}