There are plenty of wallet cases that protect your smartphone and also hold your cards. The LootLock is also worth a look. It is a super-slim, stick-on wallet for smartphones that can hold up to 3 cards or cash. The LootLock has a locking wheel to keep your cards locked-in even if you drop your phone.
This credit card holder is super slim and pocket friendly. It can be removed in a snap when you need to wirelessly charge your phone. You can get a LootLock for under $15 at this time.