I have 3 different groups with different IP addresses on different ports each have a separate DHCP server but all of them are connect to the same Switch (Non-Manageable). The issue is that these groups get mixed IP addresses i.e. sometimes Group 1 (PCs) gets IP addresses from Group 2 (IP Phones) and vice versa. How can I make them get the IP addresses for a particular group from it's assigned DHCP server instead of the other DHCP server?

Hi ,
i don't think so it could be done without Managed switch or router , your network is full bridged and not managed.
maybe DHCP client on windows has a feature could help you on this situation(just an idea)

You need to split up your broadcast domains, which requires either using separate unmanaged switches, or else a managed, vlan-capable switch.

Even if you could manage to get things sorted out in their current state, it would be bad practice. You can get older-model Cisco, HP, Dell, etc switches for next-to-nothing in the after-market. (litterally, a 2950 could be gotten for less than $100 - I've seen them as low as $50 on ebay sometimes.)

In a powerful DHCP server like the ISC one you can have different pools and match them on user defined
criteria like options, mac address range, hostname patterns, etc.
I don't think MikroTik's DHCP server can be made to do this, but you can consider installing a Linux system
and running ISC DHCP on that.