There is no installation needed to use these functions; they are part of the PHP core.
However, to enable Argon2 password hashing, PHP must be built either with libargon2 support using the --with-password-argon2 configure option or, starting from PHP 8.4.0, with OpenSSL using --with-openssl.
Prior to PHP 8.1.0, it was possible to specify the argon2 directory with --with-password-argon2[=DIR].