Okay, so you might hold off on purchasing a whole lot of stuff. You’re shooting on your phone, and it’s just you making these films. The more gear you get involved, the more distracted you’ll be in trying to deal with all of it. That makes for a pretty rough ride and can negatively affect your end product.
At the very least, look for a small tripod and phone clip so you can get your phone set up in the right places. Outside of that, the only thing you might want to deal with is your sound (if you’ll be speaking on-camera). There are two ways to go with this. You can get a small mic that mounts on your phone (such as the RØDE VideoMicro II). If you get a tripod clip for your phone that has a shoe mount on top, you can mount this mic and at least have something with a bit more directional response. Putting the mic on top of the camera is, in the grand scheme, the last place to put a mic for great dialog, but for what you’re doing it may give you enough to play around. This is the most affordable option. Otherwise, you could go for a low-cost wireless mic system like the RØDE Wireless GO II, with which you’ll also want a lavalier mic like the RØDE Lavalier GO. This is a more expensive option, but it allows the mic to be properly placed on you so that the mic is close to the dialog.
99.99% of the time, I’d avoid suggesting a camera-top mic. But we’re not talking about a typical scenario here. This is just you and your phone, and the point here is not to spend a whole lot of money on stuff that might or might not see longterm use.
That’s about it. Honestly, I wouldn’t put much more money into it than that if you’re just dipping your toe in the water to see how you like it. The VideoMicro also means that you have a mic to capture sound when you’re shooting without anyone in the picture, so you get the traffic on the highway or the creek in the mountains or the birds in the trees. And if you start making shorts and realize it’s something you love to do, and you want to get more complex (and have more people involved), then it’s time to look at more tools for the job.
As for editing, Resolve has a free version but know that there’s a learning curve. You might also look at LumaFusion, which now has a version for Android. It’s an editing app for mobile, and it has some impressive capabilities.