PHP Arrays =?= Linked Lists?

Ar arrays in PHP actually Linked Lists?

What I’m really asking is whether or not it’s a constant time operation to resize an array or is it constant time to do an array lookup.

$myArray = array();
$myArray[] = "first";
$myArray[] = "second";
$myArray[] = "third";

Does it have to reallocate and copy the stuff over each time to store it in the array?
And does $myArray[2] have to traverse the array to find the value or is it constant time?