Popular emulator GBA4iOS returned last week and should now work with iOS 9.2 and below without having to jailbreak your phone.
What this means is that you can grab GBA4iOS and use it to play Game Boy games (and romhacks) on your phone once again. Pretty nifty.
However, as always with GBA4iOS, this won't last forever as Apple release constant updates that render the emulator useless.
That said, creator Riley Testut is always working to ensure that GBA4iOS is up and running as soon as possible whenever this happens.
So, for now, you can grab GBA4iOS through its website.