Enabling Voice Only on an 877 Main Company Number

Hello. I have an 877 number as my main company number. In the Admin Portal under "Phone System --> Numbers in Use" for every other company number I get a drop-down box where I can choose "Voice Only", "Fax Only", or "Voice and Fax". For my 877 number, "Voice and Fax" is selected for me with no dropdown box options.

How do I change this 877 number to Voice Only?

I have another fax number I want faxes directed to.

Thanks,

Michael