使用str_getcsv，因为它是CSV，然后只分配第一列和第二列作为数组键，规范化它，然后一旦你有了它，你可以循环它，并建立你想要的结果。
我们的目标是让这个结构：

Array
(
    [2020-01] => Array
        (
            [Starter1] => 11,4%
            [Starter2] => 6,9%
            [Starter3] => 9,5%
            [Starter4] => 11,1%
        )

    [2020-02] => Array
        (
            [Starter1] => 5,8%
            [Starter2] => 5,8%
            [Starter3] => 10,0%
            [Starter4] => 6,4%
        )

)

您可以循环执行以下操作：

Year;    Starter1; Starter2; Starter3; Starter4
2020-01; 11,4%;    6,9%;     9,5%;     11,1%;    
2020-02; 5,8%;     5,8%;     10,0%;    6,4%;

例如：

<?php
$str = '2020-01; Starter1; 11,4%
2020-01; Starter2; 6,9%
2020-01; Starter3; 9,5%
2020-01; Starter4; 11,1%
2020-02; Starter1; 5,8%
2020-02; Starter2; 5,8%
2020-02; Starter3; 10,0%
2020-02; Starter4; 6,4%';

// normalise and group data
$result = [];
foreach(str_getcsv($str, "\n") as $row){
    $row = array_map('trim', str_getcsv($row, ";"));
    $result[$row[0]][$row[1]] = $row[2];
}

// loop over to specification
echo 'Year;    Starter1; Starter2; Starter3; Starter4'.PHP_EOL;
foreach ($result as $year => $row) {
    echo $year.'; ';
    foreach ($row as $key => $col)
        echo $col.";".str_repeat(' ', (($v = strlen($key)-(strlen($col)-1)) && $v > 0) ? $v : 0);
    echo PHP_EOL;
}

https://3v4l.org/11VaW