You are unable to select f2.4 because the lens you purchased with the camera doesn't have the capability. If you select a lens with an aperture of 2.8, 1.4, or whatever, then you could select that wide open.
It would be good to know the lens you were using as well. However you don't indicate how you feel the camera is failing - only that the image it created is not as good as the image the S9 created. This is why we need to see or understand what the difference in the images is and what result you were attempting to achieve. What settings (shutter, aperture and ISO - EXIF information) did you use on your phone? Most photo editing software will allow you to access that information which is included as part of the image.
Many phone cameras do not let you select settings and some have simplified settings. Your D5300 is fully capable of achieving equal or better images as you learn how to use it.
Post up the images and we will be happy to help you learn what went wrong then and how to try and avoid those problems moving forward.