Take the photo, edit on PC for best results, or better still good camera and lens 😉
But bokeh is all about the appealing nature of blur in an image. Best way is with a decent camera and lens, but that isn’t what you’ve got in a smartphone. Camera focused on a very close object may get the background to blur in the right way but the small sensor, basic focusing and huge depth of field makes it tricky. Other than that, any app that allows you to fake it by defocusing selective areas will give you something reasonable. Enlarging pin points of light as the blur of a lens would is harder to do. I guess there are apps for it, but don’t know.