password hashing cannot login codeigniter

You are making this a tad overly complex - the actions of the functions you are using makes little sense to put inside a function - its a simple one-liner. And password_verify() already returns a boolean true/false, so you don't need to use a ternary operator either.

Your insert can be more clear and explicit by doing the following (and removing your getHashedPassword() function),

function saveAccount(){    $data = array(       'username' => $this->input->post('username'),       'password' => password_hash($this->input->post('password'), PASSWORD_DEFAULT),       'type' => $this->input->post('accountType')    );    return $this->db->insert('users', $data);}

Then in your can_login() function, you cannot query the password in a WHERE clause. By doing that, you will never get a result back (as the hash isn't comparable through a comparison operator). You need to fetch it, and then compare the retrieved hash by using password_verify(). Calling your verifyHashedPassword() without checking the result won't magically check anything. Now, you can also remove your verifyHashedPassword() function.

function can_login($username, $password) {    $this->db->where('username', $username);    $query = $this->db->get('users');    $user = $query->result();    if ($query->num_rows() > 0 && password_verify($password, $user[0]->password)) {        return $query->row_array();    } else {        return false;    }}

Your password column should be of at least 60 characters length, although to accommodate future changes, it can be longer (for example 255 characters long).