Center all text in PHPSpreadsheet and make the cells expand to fill up with context

This would do the trick:

For autosizing (cell automatic expansion) do this:

$sheet->getColumnDimension('A')->setAutoSize(true);
$sheet->getColumnDimension('B')->setAutoSize(true);

NOTE

You have to do this individually for each column as the getColumnDimension method can only accept one column as it's parameter.

You have already figured out the horizontal alignment, but it is worth noting that you can set the alignment of more than one column using one command.

$sheet->getStyle('A:B')->getAlignment()->setHorizontal('center');

As for setting the cells values, I would prefer you do it separately from anything that has to do with formatting and styling just for the purpose of separation of concerns and readability.

Cheers.

For autosizing a range of columns:

foreach(range('A','Z') as $columnID) {
    $sheet->getColumnDimension($columnID)->setAutoSize(true);
}

Set the info in every cell to be centered:

$alignment_center = \PhpOffice\PhpSpreadsheet\Style\Alignment::HORIZONTAL_CENTER;

foreach($sheet->getRowIterator() as $row) {
    foreach($row->getCellIterator() as $cell) {
        $cellCoordinate = $cell->getCoordinate();
        $sheet->getStyle($cellCoordinate)->getAlignment()->setHorizontal($alignment_center);
    }
}

These work for:

"phpoffice/phpspreadsheet": "^1.6"