<?php

$words = array (
    1 => 'Sports',
    2 => 'Camping',
    3 => 'Climbing'
);

$parts = explode(',', '1,3');

for ( $i = 0; $i < count($parts); $i++ )
{
    $parts[$i] = $words[ $parts[$i] ];
}

print_r($parts);

Array
(
    [0] => Sports
    [1] => Climbing
)