dont use boolean if ur modeling it for production type modeling i check u r model and they so much booleans i recommend use chamfer vertex to convert a 1 vertex to quad and apply bevels to the corner of edges to create a good mesh so after doing this press 3 for smooth view u see a quad now turning in to the cylinder shape also do major things like break a single asset to multiple thing model it for ex ur iphone button u have just extrude it which creating so much connectivity of triangles and u just keep wasting ur time in converting them into quads so i recommend to create a button in a new mesh and then put them back so that it feels that buttons are attaches to it by insisting the extrude too much that s it also try crease tool for smoothing the bevel of frame of iphone that it