If i purchased one license does that mean that the admin can have a phone license plus another user or only the admin can use the phone license?
If you have 1 phone license under your account, this can be applied to any 1 user on the account. This could be either the admin or another user. To have both an admin and another user have access, this would require 2 licenses.
If the admin is included in the count, how was I able to assign another user with a phone license, does it add automatically and I am charged?
You will need a license for each user, including the admin, if you wish for them to have access to Zoom Phone.
The API returns that I have 1 available license and 0 assigned, but how is this the case if I used up all of the licenses?
To clarify, is the Zoom Phone license assigned to the account admin or a user yet? This can be done following the instructions here.