На коленке.
function getDatesForThisAndNextWeek()
{
$days = ['Monday' => 1, 'Tuesday' => 2, 'Wednesday' => 3, 'Thursday' => 4, 'Friday' => 5, 'Saturday' => 6, 'Sunday' => 7];
$i = 1;
foreach($days as $k => $v)
{
$today = new \DateTime();
$today->setISODate((int)$today->format('o'), (int)$today->format('W'), $days[ ucfirst($k) ]);
$daysArray[ $i ] = $today->format('Y-m-d');
$todayPlusWeek = $today->modify('+1 week');
$daysArray[ $i + 7 ] = $todayPlusWeek->format('Y-m-d');
$i++;
}
ksort($daysArray);
return $daysArray;
}
var_dump(getDatesForThisAndNextWeek());