If you're lucky the problem might be something like the wire attaching your LCD/digitizer to the motherboard was knocked loose and it requires opening up the phone and re-seating the connector. But that also depends on what model phone you have, some models are relatively easy to dis-assemble and re-assemble, some are notoriously difficult where the manufacturers used glues and adhesives instead of mechanical fasteners (screws). Also some models have combined display and digitizer assemblies, some are separate. In this instance unless you state which model phone you have, it's hard to give any details more specific.
A potentially more costly iissue might be the digitizer itself was damaged, but again that depends on which model. Some will be less expensive to replace, some be much, much more involved (and expensive) to replace. Could also be a matter where a solder joint on the motherboard was jarred apart. But for a more accurate appraisal, you'll need to have someone actually look at your phone.