About Combine Variable inside loop

Question

using php I have these Variables

$pl_1 = 2;
$pl_2 = 14;
$pl_3 = 442;
$pl_3 = 15;
$Count = 4;

I used for loop to get them

for ($x = 1; $x <= $Count; $x++) {
echo $pl_.$x;
}

It doesn't work how it's done