Now that you want to become a good photographer with your cell phone, here is a great idea I have learned from all professional photographers:
When starting out, take pictures of all types of things. Somewhere you will find out that you like to take pictures of _________ (something). And you are not too bad either. You have taken some reasonably good photos.
And once you have discovered a subject that you like, and it seems that you are naturally good at it, then the next step is to take a lot of pictures of that subject.