There is a slight bug in iTunes Match that doesn't update playlists on your iDevice. Although this is annoying and will most likely be fixed by Apple in the next update, here is a quick solution to solve it. Note: Sometimes there is a delay between what is on your computer and what is on your iPhone. Wait a few hours and the sync should catch up, otherwise, continue reading the steps below.
Step 1) On your device, go to Settings > Music > iTunes Match.
Step 2) Turn iTunes Match to "OFF."
Step 3) Wait about 5 minutes, then open the music app and confirm that no music is showing up there.
Step 4) Go back to Settings > Music > iTunes Match and turn iTunes Match back to "ON."
Step 5) Wait for iTunes Match to sync and your playlist should now be there.
Annoying but that's the fix!