Understanding Errors in Public Key Authentication

I'd like to authenticate the public key using the ssh2_auth_pubkey_file function in PHP.
I am having a hard time because I cannot authenticate with the following message.
If you have any advice such as whether this is the cause, please take care of it.

$connection=ssh2_connect($host,$port);
if(!$connection){
   // connection failure
}

$user='user';
$pubKey='/home/user/.ssh/authorized_keys';
$priKey='../id_rsa';

if(!ssh2_auth_pubkey_file($connection,$user,$pubKey,$priKey)){←★Error here
   // authentication failure
}

Warning Error: ssh2_auth_pubkey_file():Authentication failed for user using public key:Unable to open public key file

The public keys are placed below, each permission is 755, .ssh is 700 and authorized_keys is 600.
/home/user/.ssh/authorized_keys

*Public key authentication is available from TeraTeam.