$re = '/\\\\.+?(?= \|)/i';
$str = '| Area | vserver | file-id |connection-id | session-id | open-mode | path |
| manphsan01 | manphs101 | 9980 | 4278018043 | 5065142205921760710 | rw | Share01\\Mandaue\\Data01 |
| manphsan01 | manphs101 | 1790 | 4278020659 | 5065142205921763223 | rwd | FinanceDept\\ARCHIVING |
| manphsan01 | manphs101 | 1824 | 4278020659 | 5065142205921763223 | rwd | Share01\\Cebu\\Year2022 |
| manphsan01 | manphs101 | 1976 | 4278020659 | 5065142205921763223 | rwd | SGSDept\\General\\Document | more |
';
$subst = "";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php