Using the generated file from the tutorial Create Xlsx Files With Different Cell Background Colors, learn how to merge cells in PhpSpreadsheet.
Requirements:
- Composer
- PHP 7.2 or newer
Before Cell Merging

Step 1.
Setup dependencies.
{
"require": {
"phpoffice/phpspreadsheet": "^1.3"
}
}Step 2.
Install phpspreadsheet.
$ composer install
Step 3.
Create a new PHP file, and start coding.
<?php // Autoload dependencies require 'vendor/autoload.php'; // Import the IOFactory class use \PhpOffice\PhpSpreadsheet\IOFactory; // Import the Xlsx writer class use PhpOffice\PhpSpreadsheet\Writer\Xlsx; // Full path of the file to be indentified $inputFileName = 'create-xlsx-files-with-different-cell-background-colors.xlsx'; // Identify the file type using the IOFactory object $inputFileType = IOFactory::identify($inputFileName); // Create the reader object $reader = IOFactory::createReader($inputFileType); // Load the file to read $spreadsheet = $reader->load($inputFileName); // Retrieve the current active worksheet $sheet = $spreadsheet->getActiveSheet(); // Merge cells from A1 to D5 $sheet->mergeCells('A1:D5'); // Write a new .xlsx file $writer = new Xlsx($spreadsheet); // Save the new .xlsx file $writer->save('merge-cells-in-xlsx-files.xlsx');
Test.
Run the following codes.
$ php merge-cells-in-xlsx-files.php
Result.
Open the generated file merge-cells-in-xlsx-files.xlsx.

References:
How to install PhpSpreadsheetOn this site
Create Xlsx Files With Different Cell Background ColorsOn this site
Read Xlsx Files Using IOFactory ClassOn this site
Creating a spreadsheetphpspreadsheet.readthedocs.io
Reading and writing to filephpspreadsheet.readthedocs.io
Reading Filesphpspreadsheet.readthedocs.io
PhpSpreadsheet Recipesphpspreadsheet.readthedocs.io
Merge/unmerge cellsphpspreadsheet.readthedocs.io