Two ways to reduce the size. Either number of pixels, or number of colors. To reduce the overall size by either cropping off unneeded edges or shrinking from say 1600 X 1200 to 800 X 600. Another choice is to keep the number of pixels large, but reduce the number of colors and that's accomplished by saving the file as a GIF rather than a bitmap or jpeg.
Text it to yourself. The phone will compress the file. Save and post the incoming image. It will be smaller.
I use a third party image hosting site. It resizes when it up loads. Then the pictures are available on any of my devices that have internet. It also saves storage for the forum. That counts at the other place I post.
I just don't post pictures here anymore. Too many hoops to jump through. It won't let me upload them directly and it doesn't show up if I try to add them from a link.
Man, we sure have come a long way from the days when my Dad would use a "Darkroom"(as he called it)to develop his own pictures taken from his Nikon.
I hope to see the Westminster dogs do that as they perform their Obstacle Course skills this week-end. Not going live, I mean on TV.
There are loads of free image resizers..irfanview is good, have a wee search and find one you like. Robert.