Maybe there's a way to pull the images off the phone to a computer and stack them, depending on format, or someone has made an app to do it. I'm sure there are people here who know more about it than I do. Still, they're great images for single shots, just keep working on getting the best focus and doing things like remotely triggering the camera will really help.
What you said about the brightness and shutter speed is interesting. You want the fastest possible shutter speed and lowest ISO to try and get a sharp image. That's probably easier with a dedicated astro cam or DSLR where you have more control. The other issue is the seeing which will cause the moon to "wobble" a bit and make focus harder. Stacking would help with the former.