Jerry wants to record webinars and wants to know if he can use an external microphone to do it. Leo says he could, but you'd need an adapter for the minijack on the phone. He recommends just using the microphone on the phone. It'll work fine for that. He could take the direct out of the computer using the PC's headphone jack, and then plug that into the jack on the phone. That should bypass it altogether. One other option is to get a directional mic that will plug into your phone as well. Or even a parabolic mic. RODE makes great models with minijack connectors. The VideoMic line is ideal and he can even get a handheld grip.
Leo also says that a Beachtek adapter will take those XLR based mics and adapt them to Minijacks with unbalanced sound.