Another thought is that at times with a phone (and perhaps tablet?), even when you are using a browser on the phone, once you try and open content like a conference talk, it may try and do that using the Gospel Library App instead of remaining in the browser. Generally this is an option you get the first time you try and access that content, and it remembers (if you select that option) your preference. All that to say that perhaps the issue comes from your phone/tablet browser trying to open Gospel Library, and something is going wrong at that point. You might try uninstalling Gospel Library and then trying to access the content to see if that helps.
And if you are truly trying to access the content on your iPhone through the church website and not through the Gospel Library App, I'd definitely suggest directly using the app instead of trying to go through a web browser to access content.