Depth of field will always be one of the biggest challenges for a smartphone camera. Wide angle lenses and tiny sensors make any substantial background blur difficult to achieve. But faking it almost always makes things worse.
First, blur added with an editing app is usually applied uniformly across most of the frame. Thats not the way a lens works, so it looks unnatural.
Second, its hard to be precise when selecting the object you want in focus so you can end up with harsh transitions from sharp to blurry. Its distracting and a dead give away that youve been messing with the image.