Network confusion!

Trying to sort out my uncles business network

Alright guys.... got roped into helping my uncle sort out his business IT situation. His initial complaint was his cameras would come in and out (they do) but I believe his problem has to do with DHCP or DNS. Here’s his setup: ISP -> ARRIS MODEM->edgerouter lite -> unmanaged tp link 16 port switch -> port 15 goes into a mikrotik router board, and port 16 goes to a ipscom phone switch(?) and than the mikrotik router has 2 small cables going to the ipscom phone switch. Basically Im in way over my head but I would like to help my uncle figure this out he got quoted something like 25k for a total rip out and redo but I feel like he has all the equipment he needs already just needs to be better configured. I’m screwed lol

Wish I took some better pics but you sort of get the idea lol. I can plug a pc directly into the mikrotik board and get internet but if I unplug the mikrotik the phones break is the mikro just supplying PoE? Anyways thanks to anyone who read this and possibly feels bad enough to help