На основе одного из других решений с флажком для переключения между неделями, начинающимися в воскресенье или понедельник
function getWeekForDate($date, $weekStartSunday = false){
$timestamp = strtotime($date);
// Week starts on Sunday
if($weekStartSunday){
$start = (date("D", $timestamp) == 'Sun') ? date('Y-m-d', $timestamp) : date('Y-m-d', strtotime('Last Sunday', $timestamp));
$end = (date("D", $timestamp) == 'Sat') ? date('Y-m-d', $timestamp) : date('Y-m-d', strtotime('Next Saturday', $timestamp));
} else { // Week starts on Monday
$start = (date("D", $timestamp) == 'Mon') ? date('Y-m-d', $timestamp) : date('Y-m-d', strtotime('Last Monday', $timestamp));
$end = (date("D", $timestamp) == 'Sun') ? date('Y-m-d', $timestamp) : date('Y-m-d', strtotime('Next Sunday', $timestamp));
}
return array('start' => $start, 'end' => $end);
}