I had a problem with my iPhone case that really affected the front camera and ended up causing really bad flare.
Obviously this is partly down to which iPhone you have, so I've listed a few different cases YOU NEED to check out for each model:
iPhone 6+ cases
http://store.apple.com/us/product/MGQV2ZM/A/iphone-6-plus-leather-case-midnight-blue
iPhone 6 cases
http://www.pure-gear.com/shop-by-device/iphone/dualtek-extreme-shock-case-for-iphone-6.html
iPhone 5s cases
https://www.vysk.com/privacy-charging-case (this case CHARGES your phone AND adds extra security..)
iPhone 5 case
http://www.ebay.com/itm/Bling-crystal-Rhinestone-iphone-6-6-plus-4s-5-5s-5c-6-case-cover-blue-3d-gems-/131338130638?roken=cUgayN&soutkn=nY6Sn4 (if you like OTT bling cases)