$re = '/Passphrase=\K.+?(?=\\\\n)/m';
$str = '[wifi_d0b5c2bc1d37_7078706c617967726f756e64_managed_psk]\\nPassphrase=testpasssword\\nName=pxplayground\\nSSID=9079706c697967726f759e69\\nFrequency=2462\\nFavorite=true\\nAutoConnect=true\\nModified=2018-06-18T09:06:26.425176Z\\nIPv4.method=dhcp\\nIPv4.DHCP.LastAddress=0.0.0.0\\nIPv6.method=auto\\nIPv6.privacy=disabled\\n';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
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