The usual way to do that with PCs plugged in via the phones is to configure the phones to tag their traffic on a VLAN, and only have that one DHCP server on the VLAN for the phones.
There is no option to ignore a group of MAC addresses, closest is the deny unknown clients option mentioned. That's true of every DHCP server, it just isn't possible. The only other alternative is to configure whatever DHCP options the phones require so they don't have to hit their own DHCP server, which may or may not be a reasonable solution depending on specifics.
If you can't change the phones to tag their traffic, and can't plug the PCs in elsewhere, and can't consolidate to a single DHCP server, you have an unsolvable problem regardless of what software you use.