There is no way a retroactive thing happens. Let me make a list and explain.*
You have an artboard of 1080x1080px.
I do not have an Illustrator right now to confirm if I need this step, but it is a good practice.
Make sure no element is outside the artboard. Hide whatever exceeds the artboard with a clipping path. And also, if you do not have an element all the way to the edge, you can also add a transparent (or white) rectangle as a background on all your post so you make sure you really have 1080x1080px.
In Illustrator you should not change the resolution of the dialog box. Leave 72PPi and you will have a file of 1080x1080px.
Now, you need to view this image on another program. It can be a web browser. Any program that will open it at 100% and show you the dimensions.
Here is your image and it is not 1080x1080px. It is 833x582px
If you are on windows you can use Irfanview as an image viewer.
If the image is wrong in this step, go back to your artboard (step2) and fix it.
If the image is really 1080x1080px continue. The image is fine, and there is no way anything previously done in Illustrator will retroactively modify this image.
You send your file via Bluetooth. If the software is really only for transferring files it should not compress them or resample them.
When I view on my phone image quality is fine but on my 16 inch laptop its a bit blurry
You view it on your phone and it is ok. But this part I do not understand. If the image was ok, and I assume you have Illustrator on your 16 Inch laptop and was fine, how now is blurry. After doing what?
If everything is ok up to this point, upload to your social network.
Keep in mind that all social networks will compress your image because they need to save space for images that will potentially be viewed millions of times, so they compress them when you upload them.
You can not do anything except prepare them to exact dimensions so you do not give any excuse for a resampling. They will be compressed but not resampled.
In your example, the font is too small, and you can also add a bit of sharpening.
But it has not a square proportion. So, you either did not prepare it right from start or you cropped it somewhere.