MikroTik

Hi guys. I am setting up a mikrotik is a sub office for the purpose of failover. The sub office will utilize the main office network for internet then use an LTE router as failover. I have a problem now as they are using voip phones which use another mikrotik as the gateway which sits in the main office. there is 1 long cable running to the sub office which is where I am installing the mikrotik used for failover. The phones are all static and on a different IP range, how would I go about setting up a route so the phones will be able to see their mikrotik/gateway? Both the main office and sub office use the same phones system.

Main office Gateway: 192.168.1.1/24
Sub Office Gateway: 192.168.10.1/24
Phones Mikrotik Gateway: 192.168.222.1/24