that's normal. there's no point having a EV preset if you are manually adjusting iso and shutter speed. the f stop on the phone is fixed.
you have read a bit on basics of photography. any basic books on exposure or online will help.
Digital Photography and Exposure - For Dummies
the holy trinity to exposure is ISO, f stop, and shutter speed. EV control dial preset on the phone can only change iso or shutter, since f stop is fixed. so if you are manually adjusting ISO and shutter, you are effectively setting the EV yourself manually.