There’s nothing bad about using your iPhone to record your videos. Use it as your main camera, or to record a second angle while recording with your DSLR.
Filmic Pro is the app to take control of your iPhone’s camera.
It gives you the much needed manual controls over exposure and shutter and also lets you adjust the video quality settings.
If you’re recording video on your iPhone regularly, Filmic Pro is a no-brainer.
You can even remote-control your iPhones recording with another iPhone or iPad, using the remote app. This lets you start and stop the recording and control if everything fits into the frame.
I recommend you save some dollars and go directly for the bundle.