How to hide manager password from user on web app?

I am creating a web app on a LAMP stack where I have users with their own logins and passwords. Typical users of the application have limits on operations. For example they cannot approve an order over $5000. If there is an order over $5000, they have to get a manager to come to their desk and enter in his/her username and password to approve the order.

I can easily create a form for the manager to enter his/her credentials into an HTML password input, but here is the problem. When the manager enters their credentials into the browser, the password field is hidden from the user. But when the form is submitted, the password is transmitted in clear text. In theory, a user could get the password by using F12 or by looking at the POST.

I wanted to hash the passwords before submitting the form, but the problem is that PHP stores the passwords using BCRYPT, and javascript can only digest with SHA.

So basically my question is. How can I ensure that the manager password is hidden from the user and they cannot get it?