Hey there SoapsbyKelsey,
Sounds like your iPhone is stuck in Headphone Mode. If you Google the internet on "iphone stuck in headphone mode", you will find tons of posts and more suggestions than one can count. Some suggestions are a bit out there and others seem to be a bit safer. The cause can be anything from a dirty jack or connector or both. Some people have resolved this issue by doing a "hard" phone reset. Others have simply cleaned the lighting connector and phone jack. Several people said that simply plugging in a headphone and then trying it and then unplugging it fixes the problem. Seems the solutions are all over the place so it's difficult to figure out what the magic fix is. It's even possible that the magstripe reader it self has an issue. As you can tell, there's no way other than trial and error testing.
From personal experience, you may want to consider the Contactless Chip and Tap Reader - yep, it's a small investment but, it works well, connects to your device via Bluetooth and you don't have the liability concerns that come with "Swipes". What this means for you as a seller is that there has been a liability shift . If you swipe a chip card rather than using a chip reader, you are automatically liable for any fraudulent transactions.
Another option that's available is you can accept Tap to Pay with just your iPhone - no additional hardware. See this. Although this feature does work, it can be finicky once in a while (just a heads up), you don't want to have "multiple apps" open and running on your phone while accepting cards. Keep it simple !!
