Hi
The screen on your iPhone is covered under Apple's Limited Warranty against defects in materials and workmanship, but not against accidental damage.
Apple advises that you should not continue using a damaged iPhone. Follow the instructions here to arrange for your iPhone to be inspected and to establish your available service options (which may include mail-in service, if required), timescale and any cost:
- US: iPhone Service Answer Center - Apple Support
- Elsewhere: Apple - Support
Apple's screen repair prices vary by country. Prices in the US, for example, are detailed here (the cost may be less if you have previously purchased AppleCare+, depending on any claim history):
iPhone Service Pricing - Apple Support
To check your service and support coverage: