Large aperture does help create shallow depth of field, but phones have very small sensors and very short focal lengths, which naturally give a very deep depth of field. So a phone usually can’t produce strong optical background blur the way a larger-camera system can.

A second camera can help by viewing the scene from a slightly different position. Software compares the two images to estimate subject distance (a depth map), then applies simulated background blur for portrait mode.

So, in dual-camera phones, the second camera is not simply “for distant objects” while the wide camera is “for close objects.” In your example, the wide and telephoto cameras are different focal lengths for different fields of view, and the dual-camera setup can also help the phone calculate depth for portrait effects.