There are a lot free apps out there, where you can rezise photos taken on your phone, with no other devices needed. Let me know if you need suggestions.
BD - if you open any picture in paint. Click on Resize -> Select Pixel -> Change one number to lower (for example from 1200 to 600) then second will lower itself automatically. Save the file, File Size will be smaller. If still too large then repeat again. That is how you make size smaller and save in JPEG.