As an Account Admin or a user with Manage Users permission you will be able to access the Enterprise Phone Numbers section by going to the Company Settings, choosing the Manage Users tab and then clicking on the Enterprise Phone Numbers sub-tab.

In order to request the enterprise phone number,  you will need to select the users you want to get the Enterprise Phone Numbers for and lick on the Request Enterprise Phone Numbers button. 

If you wish to request an Enterprise Phone Number just for a single user, you should go to the top right part of the User's row, click on the More menu and select the single Request Enterprise Phone Number option. 

Once the Request button is clicked on, a popup will appear, where you will need to select the country you want to get the numbers for. Click on the Save button and the request will be sent. 

Please give it some time until the numbers are obtained. You will notice the numbers in the numbers section once they are acquired successfully. 

There is also an option to Delete a phone number for a single or multiple users. For a single user, you can just click on the Delete option in the More menu and for more users, you can use Delete bulk action.