Welcome, nvoharj!
For shooting with an iPhone, Filmic Pro is an absolute must. So, well-done jumping in with that! Don't forget that you can also set your time base (the frame rate you'll use formediting and playback). Choose your frame rate based on the aesthetic you want: 30p and 60p will look like NTSC video/news. 25p and 50p will match your BBC broadcasts. 24p will look like motion picture (the movies).
Now, to your video:
Most of the shots go on way too long, and it's hard to judge this as an edit since the shots seem too disjointed to tell a complete story. I get that you were playing with slow-mo in the first shots, but they were wides that had nothing else to support them. When you hone in on something, look at it from different distances and different angles. Get close-in on details you'd normally pass by, and that the viewer would never see in the wide. The feather caught in the potted plant would have been interesting very close-up.
For your painting, perhaps look at shots that set the viewer into that scene before you go into the time lapse: explore the "before" and maybe even bring the supplies in (paint bucket and brush) as part of the visual story.
And don't neglect sound! A mixture of "nat" sound (recorded with the video), pre-recorded environmental sounds and, if you like, some music can help set the scene and draw the viewer in.
One challenge with iPhone shooting is the Jell-O vision, an artifact of a rolling shutter, where parts of the image jiggle as if looking at them through a block of Jell-O. Your slow-mo shots have exacerbated this. The best way to avoid it is to steady the camera, and your handheld work is very shaky. For reference, see the POV shot at the end. From your shadow, it appears that you do have some sort of handle attachment, so whenever possible hold it with both hands. Tuck your elbows into your sides to provide added stability. A tripod and iPhone tripod bracket are also advisable.
Play with lighting angles, too. You were working with the sun, so you're stuck with it wherever it is, but it was backlighting most of your shots with a little too much of it creeping into the background. This causes everything in the shadows, which is what you exposed for, to be washed out. Another challenge with iPhone, much like DSLR, is shooting with a very compressed codec. That means pushing the color grading in post can also make the images fall apart because there's not a whole lot of data to begin with. So you want to start with as much information as you can, which means proper exposure across the entire luminance range. So, shooting directly into the sun is generally bad (with exceptions), but putting the sun at a slight angle in the background can yield intersting (and useful) results.
Keep it up, man! Practice, practice, practice! You'll be amazed at what you can do with the iPhone and Filmic Pro, and the app gives you plenty of learning tools for proper exposure!
