FAX /Phone - how to use phone but receive fax when needed - Dell printer

I have a Dell c3765dnf and I hooked it up to our 2nd business line.

I need to figure out how I can still use the rollover feature on our phone on the 2nd business line,  and receive faxes only as needed.

Right now, If we are on the phone on our first line, and a 2nd call comes in -instead of it ringing on our 2nd phone line, the fax answers it.

Is there a certain setting I need to use?