I've been using Delta for a long time and the easiest way I've found to load your Game Boy cartridges onto your iPhone is with a handy little Mac accessory called the GB Operator.
I wrote about how it works on [@macstories](https://mastodon.macstories.net/@macstories)…
https://www.macstories.net/stories/how-to-load-your-game-boy-games-onto-the-iphone-to-play-in-the-delta-emulator/