Extending DHCP

I’m getting ready to install a Voice/IP phone system.
I have a network (192.168.1.x w/ 255.255.255.0)
While I have space for systems, the phones need to be logically addressed, so I need to double the number of hosts.
Can I simply change the maskto 255.255.0.0 and add another network such as 192.168.x.x?

Thanks!