Resizing jpegs, limiting file size

Hello All, I am wanting to cut the file size of photos from my phone. I have tried opening in GIMP, but takes a bit of mousing and clicking around, and even saving/exporting several times to get the size down. I think the imagemagik suite should be able to do, but my reading of the man pages does not make it apparent to me. They talk of resizing, but it looks like the linear extent, rather than loosing some detail of the same extent of image. I would appreciate any contributions. regards, Mark Trickett