What is the best way to create XLS file in PHP

its pretty easy, because excel supports html code. So you just need to add a header in the top of the file.. and then echo your html code!

header ( "Content-type: application/vnd.ms-excel" );
header ( "Content-Disposition: attachment; filename=foo_bar.xls" );
echo "<table><tr><th>Header1</th></tr><tr><td>value1</td></tr></table>";

this will generate an excel file!

Depends if you want a CSV file or an XLS file. An XLS file can include formatting information for the cells, as well as row/column locking, protections and other features that are impossible in a CSV file. Also, keep in mind that Excel does not correctly support UTF-8 encoded content when opening CSV files.

If you want a formatted XLS file, then you need a library such as PhpSpreadsheet that can write a file with that formatting, or COM if you're server is running on Windows with Excel installed