The openssl example is completely wrong. The public key must be extracted from certificate and openssl_pkey_export() is for private key only.
Working example:
<?php
$publicKey = openssl_get_publickey(file_get_contents('certificate.pem'));
$details = openssl_pkey_get_details($publicKey);
file_put_contents('my.phar.pubkey', $details['key']);
?>
No need to say that the best and strongest encryption of my.phar/.phar/signature.bin is useless if the consumer does not check against a valid fingerprint or certificate of public key as anybody can open, read, recreate and sign a new archive with new key. Do you do? Think about it.
