I have outlook (both personal and work), gmail (both personal and school), comcast, and email apps on my phone. On every single client, whether in-browser or mobile app, I have to click "load images" when I open an email or they won't load. It's been like this for years. Idk if the iPhone email app is different since I have a Galaxy but I imagine not. I admit I'm assuming this feature is disabled by default purely based on my anecdotal evidence though.