How to transfer IP phones to a new vlan in parts?

Question

Network administration

Green circles are IP phones.
The task is to transfer phones to a new vlan.
Now there is a flat network 192.168.1.0/24 (default-vlan in D-Link terminology), in which IP phones (physically) exist - 192.168.10.0/24. There are two automatic telephone exchanges, as I could draw it in the picture.
How can I transfer phones of a certain node (for example, U1) to a new vlan without losing connection with those remaining in the old one and with PBXs?

Answer 1

1) find the ports in which the PBX and IP phones are enabled
2) raise the interface and dhcp (or somewhere) on the gateway
3) Select the necessary ports and transfer to the newly created vlan
or what is the difficulty?