Some new tips, based on recent experience. I've found that putting a decent smartphone within inches of a PA speaker cabinet can create pretty decent quality recordings. The two things I'd suggest are (1) make sure there's a way to control the input volume so the recording isn't blown out and (2) find an app that records high quality audio, and can handle the length of the audio you plan to record. Don't be scared to put the recorder right next to the speaker, it really helps cut down the other ambient noises in the room. As you get farther away, the nervous tapping of someone's pen and the room's air conditioner may become larger parts of your recording than you'd like.
I've been using an old iPhone 4S to record presentation audio. I think the recording quality with the built-in mic sounded a bit better than the iPhone 5S (the only two phones I tested). And I used the pay version of the Rode Record app. It's a little flaky and weird to figure out, but it's come through on three nine-hour-recordings at Bitcoin conferences.
However, the Rode Record app had me cursing at it last night. The app makes you create an audio file first, then it can be transferred to your computer. However, the native app file and the export files for my nine-hour recordings are massive and time-consuming to process on the phone. But my most recent recording at KEYNOTE 2015 became impossible to export from the Rode Record app. Fortunately I found that others have dealt with the issue, and figured out how to extract the native audio file using a combination of iExplorer and Audacity. So, if the Rode Record app ever stymies you, Google the issue and you'll find the steps to save the audio. That method seemed so much better, that the next time I have an all-day recording, I'll probably use the workaround rather than have Rode Record create the audio file for export.
BTW, a direct line from the sound board at a conference will sound best, as opposed to mic-ing a speaker (especially if you can get accurate levels). But so far, 2 of 3 conferences have not allowed access to the sound board.
