I found Daniel Holloway’s post
I used nano on /etc/sysconfig/network-scripts/ifcfg-eth0, changed the static ip address that was still configured for the one occupied by the network printer (DHCP), and rebooted.
And it works!
This time I have the Pbx’s static IP set for an address range that is not used by the router’s DHCP. Shouldn’t have any conflicts going forward. Shouldn’t have set myself up for this possibility in the first place.