<?php

$array = [1, 2, 3, 4, 5];
$factor = 2;

function multiplica($array) {
    
    $factor = 5;

    $array = array_map(function ($value) {
        global $factor;
        return $value * $factor;
    }, $array);
    
    return $array;
    
}

print_r(multiplica($array));