<?php   

function inclineWord($number)
{
    $arrWord1 = array(1);
    $arrWord2 = array(2,3,4);
    $arrWord5 = array(5,6,7,8,9);
    foreach ($arrWord1 as $arr1) {
        if ($number == $arr1) {
            return "рубль";
        }
    }
    foreach ($arrWord2 as $arr2) {
        if ($number == $arr2) {
            return "рубля";
        }
    }
    foreach ($arrWord5 as $arr5) {
        if ($number == $arr5) {
            return "рублей";
        }
    }
}
$result = inclineWord(1);
echo $result;