Using str_replace with array gives unexpected results

I have an array of numbers, something like 1,2,3,4,5,6,7, etc. These are IDs stored in a database.

I have a group of labels that I am trying to apply to these numbers for use later on, but my output isn't showing what I expect. For instance, I have this:

$ids[0] = 7, $ids[1] = 4

which, I use this to apply the labels:

$ids = str_replace('7', '1Mbps Internet', $ids);
$ids = str_replace('4', '2Mbps Internet', $ids);
$ids = str_replace('1', '3Mbps Internet', $ids);
$ids = str_replace('8', 'Commercial Internet', $ids);
$ids = str_replace('12', 'Tower Friends', $ids);
$ids = str_replace('6', 'Cable TV', $ids);
$ids = str_replace('11', 'Cable TV Basic', $ids);
$ids = str_replace('5', 'VOIP', $ids);
$ids = str_replace('10', 'Web Services', $ids);

However, my output is looking like this:

3Mbps InternetMbps Internet, 2Mbps Internet

When it should come out like this:

1Mbps Internet, 2Mbps Internet

Which, that code is as follows:

$Package1 = $ids[0]; 
$Package2 = $ids[1];
$Package3 = $ids[2];
$Package4 = $ids[3];

if (!$Package1) {$P_word = "$Package:"; $Packages = "None Subscribed";}
else if ($Package1 && !$Package2) {$P_Word = "Package:"; $Packages = "$Package1";}
else if ($Package1 && $Package2 && !$Package3) {$P_Word = "Packages:"; $Packages = "$Package1, $Package2";}
else if ($Package1 && $Package2 && $Package3 && !$Package4) {$P_Word = "Packages:"; $Packages = "$Package1, $Package2, $Package3"; }
else {$P_Word = "Packages:"; $Packages = "$Package1, $Package2, $Package3, $Package4"; }

I am really unfamiliar with PHP, but it seems like it should be working. Is there something I am missing here?

Thank you.