Put nail polish on your broken phone screen and watch what happens
Sad news though — nail polish cannot repair a shattered screen. Basically, it can only fix a small crack — or at least stop it from spreading. What you should do, if you pick up your phone only to find that what once was your screen is now a spiderweb, is to take a large piece of clear packing tape and carefully smooth it down over your former screen. Will you be able to use the phone in this state? Again, no. It will just keep your phone’s innards (the expensive part) safe and intact until you can get that phone to a repair place, which you should do ASAP.
You can also, should you be the handy type, attempt to replace that shattered screen yourself, since screen replacement kits are readily available for many phone types. If you’re kind of a klutz, however, and/or this is your first time attempting to replace a phone screen and it’s a relatively new, expensive phone that you really want to save, it’s probably better that you leave the screen replacing to a professional. If you manage to mess up the screen replacement (which isn’t that hard to do) there’s a chance you could damage the phone beyond repair, so maybe practice on an old, dead phone first if you really, really want to learn DIY phone repair.