I just put together this setup and it works great.
Hanging below the iPhone is an 1k Multimedia I-Rig Pre HD. I paid 99 bucks for it at Micro Center. The I-Rig app lets you record and take video using the Iphone's front camera. I have a 6s plus, so the highest resolution i can get from that camera is 1080. It's plugged into the Direct Out on the back of the Fishman Loudbox Artist amp. The guitar (an '02 Seagull Artist Series solid Spruce/Mahagony CW with LR-Baggs I-Beam) is plugged into Channel 1 and the Shure SM58 is plugged into Channel 2. The amp is now a 2 channel mixer. I can record by setting the Gains on the amp and turning the Master Volume all the way off and just use headphones to monitor. No feedback to worry about. The Fishman's onboard effects are nice too. I cannot recommend a Fishman Loudbox or the I-Rig Pre HD enough.
I have a Scarlet Solo too, but the I-Rig Pre HD is really much simpler and more portable for me to use quickly and I can use the app to do some post processing and export to my I-Cloud drive as a finished product ready to upload to my YouTube channel.
The great thing about the I-Rig is that you dont even need an amp or a guitar with electrics. 1 good microphone (mine is a low budget AKG P120) is all you need which is what I did here.
http://www.acousticguitarforum.com/f...d.php?t=500842
The I-Rig supplies phantom power so you can use a condenser mic. The downside of that setup is it didn't pickup my vocals (so i didn't post that take) very well due to the mic placement. That's one of the things that is great about the Fishman amp. Multi channel balanced inputs and a direct out!