i'm not a pro but have been playing around for a few years now & these are the tips i can give you:
first trick is how you're uploading the pics, try linking a full size file via google drive etc rather than uploading at full size. when you upload to social media or here it automatically downgrades the size & loses quality. the other option is to reduce the size of the pic yourself, with something like photoshop, but this also sharpens the image which will give you a pixelated effect (jpeg artifacts). i would also suggest you get rid of any post processing ie filters or auto sharpen etc & rather do it via photoshop or similar, that way you can sharpen less, to accommodate the extra sharpening when downsizing the image.
other general tips, dont zoom in, unless you have optical zoom - find out whats the max for optical for your phone. rather crop a larger image to create the 'zoom' which will help with image size as well. set autofocus to focus on the silhouette, you want clean lines. look at foreground & background as well as the subject & change your focal point when taking multiple images, so you can see the effect that the focus has on the end image ie tap the center of the flower, then the tips of the pistols on top etc. you need to compose each image. for example on the image above, the fan leaves that are somewhat in the foreground, drop your angle closer to them which will create whats known as a leading line, it will effectively pull the eye into the image & at the subject. focus on the centre of the flower & use something to break the background colour, to give you a crisper silhouette. either black cloth, white paper, or something with texture(or even the sky), but if its a board, cloth or paper, hold it as far away as possible from the cam that will still keep the edges out of frame & it 'the background' out of focus.
All that being said, you'll never really be able to compete with a DSLR, so if you're serious about your photography, consider getting yourself one, you could pick them up second hand from like R1.5-2.5k. & then look into a better lense than the standard one. hit me up if you need advice on anything else.
example of an upload issue:
upload:
Link: