It's broken. It needs to be fixed or replaced. This kind of damage is not covered by the normal free manufacturer warranty that every phone comes with and which usually lasts a few months or a year, but it is covered if you have phone insurance.
So if you have insurance, get in touch with your insurance company and they'll tell you what to do next. If you don't have insurance, find a place near you that fixes phones and bring it there and see if they can fix it and how much it'll cost.
If you can't fix it or it costs too much to fix, remember that getting a new phone from your phone company might cost more than it did the first time - usually phones are discounted when you are also getting a new contract. Instead you might be able to save money by getting a used phone from eBay, but it usually has to be for the same phone company (so if for instance your phone was Verizon, you have to get another Verizon phone).