strtotime

$week = date("Y")."-W".date("W");
$fdate = $week;
$fdate = explode("-",$fdate);
$startYear = $fdate[0];						//2019
$startWeek = str_replace("W","",$fdate[1]);	//16

//일주일 계산
$startDate = date( "Y-m-d", strtotime($startYear."W".$startWeek."1") );	//2019-04-22
$endDate = date("Y-m-d",strtotime($startDate."+6days"));

//날짜 더하고 빼기
$day2 = date("Y-m-d",strtotime($startDate."+1days"));