Most likely, either the shift tube is damaged/broken or the screws have backed out of the lever at the end of the shift tube that the shift cable connects to. If the shift lever feels really "floppy", then you probably have a broken shift tube. You will probably have to pull the steering column down to get a good look at the shift tube and see how much play is in the shift tube bushings, check the shift tube to see if it is broken and see if the lever at the end of the shift tube is loose (shift cable lever).
A little word of caution: If you take the steering column down, be sure to disconnect the shift indicator cable first so it does not get broken. There is a tiny screw in the plastic braket that must be removed then the cable loop will simply slip off of the nipple on the shift tube arm.
Anyway, you will need a T-30 torx bit to work on the shift tube, the shift tube bushings and the lever at the end of the shift tube.
I made you a graphic below to help you understand what I am saying. Please note that it is NOT necessary to remove the steering wheel to do this, but you will need to remove the upper steering column shrouds if the shift tube bushings are loose.