Here is my solution to Add Two Numbers problem in PHP:

```
/**
* Definition for a singly-linked list.
* class ListNode {
* public $val = 0;
* public $next = null;
* function __construct($val = 0, $next = null) {
* $this->val = $val;
* $this->next = $next;
* }
* }
*/
class Solution {
/**
* @param ListNode $l1
* @param ListNode $l2
* @return ListNode
*/
function addTwoNumbers($l1, $l2) {
$ans = new ListNode(0, null);
$p = $l1;
$q = $l2;
$current = $ans;
$carry=0;
while ($p != null || $q != null) {
$x = isset($p) ? $p->val : 0;
$y = isset($q) ? $q->val : 0;
$sum = $carry + $x + $y;
$carry = (int) ($sum/10);
$current->next = new ListNode($sum%10);
$current = $current->next;
if ($p != null) $p = $p->next;
if ($q != null) $q = $q->next;
}
if ($carry > 0) {
$current->next = new ListNode($carry);
}
return $ans->next;
}
}
```