If there is one area where all phones start to show their weakness, it is in poorly lit conditions. If your shoot doesn’t require filming indoors, then opt for shooting outside, where you can make use of the world’s most advanced light source, the Sun.
If you have no choice but to stay holed up for your shoot, try to shoot near a light source, such as a window. Position your subject so this light source is at their front, which will help to bring out every possible detail and avoid your videos succumbing to a grainy mess.
You can also try utilising a reflector to direct the light accordingly - these are very cheap and easy to make. Remember, if a strong light source is behind your subject, this will lead to silhouetting which may not be the ideal effect for your video.