Job portals and application forms love a 200 KB limit, and a modern phone photo is twenty times that. Here is the order of operations that gets you under it without wrecking the image.
Most people reach for quality first and end up with a blotchy picture that is still too big. Pixel count is the bigger lever by far. A photograph at 1200 pixels wide is perfectly sharp on any screen and is a fraction of the size of the 4000 pixel original.
Reach for quality second, and stop as soon as you are under the limit. There is nothing to gain from going further.
If you have the choice of format, WebP produces noticeably smaller files than JPG at the same visible quality. Plenty of older upload forms still refuse it, so if the form is fussy, stay on JPG and lean on the width.
Phone cameras shoot at a resolution meant for printing, not for uploading. Most of that detail is invisible on a screen.
Yes. Add as many as you like and they all get the same settings.
No. It is compressed by your own browser and never sent anywhere.