Log in to MyAccount at accounts.globe.com.ph
From the Account List page, select your Postpaid account and then click on the "Manage Account" button.
That takes you to your dashboard. Click on the "Sign up for Auto Pay" link found just below the Pay Bill button.
You will then be redirected to the Auto Pay page at www.globe.com.ph/autopay. Enter the required information then click the "Add Account" button.