I have a smart contract. All what I need is to make a PHP script that will get some public data from smart contract using it's address. How can I do that? Maybe there is some libraries?
Yes, this is possible. I don't know if there are PHP libraries available, but as long as you can make an HTTP request and deal with JSON, this is pretty easy to do. See https://github.com/ethereum/wiki/wiki/JSON-RPC#eth_call.
You can send such a JSON-RPC call to any Ethereum node. Infura is a public node that you could use.