<?php

$playerA        = ['position' => 6, 'score' => 0];
$playerB        = ['position' => 4, 'score' => 0];
$totalDiceRolls = 0;
while (max([$playerA['score'], $playerB['score']]) < 1000) {
    $rolls = 0;

    $rolls += ++$totalDiceRolls;
    $rolls += ++$totalDiceRolls;
    $rolls += ++$totalDiceRolls;

    $playerScore = ($playerA['position'] + $rolls) % 10;
    if (($playerA['position'] + $rolls) % 10 === 0) {
        $playerScore = 10;
    }
    $playerA['position'] = $playerScore;
    $playerA['score']    += $playerScore;

    if ($playerA['score'] >= 1000) {
        break;
    }
    $rolls = 0;

    $rolls += ++$totalDiceRolls;
    $rolls += ++$totalDiceRolls;
    $rolls += ++$totalDiceRolls;

    $playerScore = ($playerB['position'] + $rolls) % 10;
    if (($playerB['position'] + $rolls) % 10 === 0) {
        $playerScore = 10;
    }
    $playerB['position'] = $playerScore;
    $playerB['score']    += $playerScore;

}
echo min([$playerA['score'], $playerB['score']]) * $totalDiceRolls; //920580