If you try to create a simple template in PHPExcel, insert some data and save it as a new file, you will see that conditional formatting is missing. PHPExcel is not a library for editing workbook files: you're not using PHPExcel to change only one string in a file and save it in the same state.
composer require silverslice/excel-template
Place variables in your xlsx-document as {foo}. Then replace them with replace
method.
use Silverslice\ExcelTemplate\Template;
require __DIR__ . '/vendor/autoload.php';
$template = new Template();
// open file
$template->open('test.xlsx')
// replace one variable to another
->replace('one', 'two')
// replace once more
->replace('foo', 'bar')
// save document
->save('test.xlsx');