Specific devices such as Cisco IP Phones need to boot their OS and configuration from a file in TFTP Server.
You should set devices TFTP Server manually or set this option in your DHCP configuration. Of course its easier to set TFTP Server in your DHCP Configuration.
1- Change your TFTP Server address to Hex.
In MikroTik DHCP Options configuration, you must use Hex form of IP address. for example, the Hex form of 192.168.1.1 is 0xC0A80101.
You can use these free IP to Hex converters:
2- Set TFTP Option in your MikroTik
In order to set TFTP Server address in MikroTik DHCP, follow these steps: