The PHP function produces output compatible with the crypt() function, which has not only the salt and the hash, but also includes the type of algorithm and the bcrypt cost.
This means that you just whack the hash and the password the user entered into password_verify(...) and it will tell you if you have a match - you don't have to keep track of the four parameters.
The beauty of that when a stronger algorithm comes out or you want to increase the cost factor of your passwords, you just change the hashing code and you don't have to do anything fancy to not break all your old hashes.
You can also use the password_needs_rehash(...) function once you verify to see if you should rehash the password to bring it up to the new level.
In general, using the defaults (mcrypt_create_iv() using dev/urandom for the salt and bcrypt with a work factor of 10 are specified with PASSWORD_DEFAULT in the curreent implementation) along with password_needs_rehash() will keep you up to date with no "retouch" necessary. When the default changes, password_needs_rehash() returns true, and you then rehash with the new defaults. All you need to do is make the db column wider than necessary for the current defaults to put maintenance off into the future. (The only real problem is that the hash function truncates passwords at 72 characters at the moment, which will force you to pre-hash the user value with something like SHA256 for very long passphrases.)
This means that you just whack the hash and the password the user entered into password_verify(...) and it will tell you if you have a match - you don't have to keep track of the four parameters.
The beauty of that when a stronger algorithm comes out or you want to increase the cost factor of your passwords, you just change the hashing code and you don't have to do anything fancy to not break all your old hashes.
You can also use the password_needs_rehash(...) function once you verify to see if you should rehash the password to bring it up to the new level.