download phpExcel : https://phpexcel.codeplex.com/

<?php
    //data to make csv (may be from database, form, etc)
    $dbdata = array(
                array("name"=>"name1", "phone"=>"1010101001"),
                array("name"=>"name2", "phone"=>"1010101002")
            );

    require_once 'PHPExcel/Classes/PHPExcel/IOFactory.php';
    require_once 'PHPExcel/Classes/PHPExcel.php';
    
    // Create new PHPExcel object
    $objPHPExcel = new PHPExcel(); 
    
    //setting column heading
    $objPHPExcel->getActiveSheet()->setCellValue('A1',"Name"); 
    $objPHPExcel->getActiveSheet()->setCellValue('B1',"Phone"); 
    
    //setting column body
    $i=2; //starting from row 2 bcz row 1 set to header
    foreach($dbdata as $data) {
        $objPHPExcel->getActiveSheet()->setCellValue('A'.$i,$data['name']);
        $objPHPExcel->getActiveSheet()->setCellValue('B'.$i,$data['phone']);
        $i++;
    }
    
    // Redirect output to a client’s web browser (Excel5)
    header('Content-type: text/csv');
    header('Content-Disposition: attachment;filename="export.csv"');
    header('Cache-Control: max-age=0');
    
    $objWriter = PHPExcel_IOFactory::createWriter($objPHPExcel, 'CSV');

    $objWriter->save('php://output');
    exit;
?>