In the US my mom has some old rotary analog phones that simply wouldn’t work with her new service. Had to buy her an analog to digital converter before they started working again. Most phone service comes through your internet modem now, so if they aren’t phased out yet, they are working on it.
He just told you. Assign VLAN on each individual port on your switch. Done. If your switch is unmanaged, then you need a new switch to support VLANs.