VLAN configuration information needed

We are experiencing VOIP phone issues that we just can’t seem to pinpoint. We’ve poured over the phone settings and can’t seem to find the culprit there. Some (not all) phones reboot a couple of times a day without warning. I have run pings to numerous phones, switches, printers and computers and when the phones drop, PCs and printers stay solid. There are some POE switch ping drops, but not to the degree as the phone drops and no rhyme or reason to what switch may drop a couple pings and what phones stay up or go down. Our phone vendor believes that a VLAN for the phones would be the path we should take. Below are some questions about how best to set it up.

1. The majority of the POE switches are Netgear GS752TPv2 (layer 2/3) and the majority of data switches are Netgear GS752TS. They have the out of the box configuration where VLAN 1 has all ports as untagged.
2. If we set up a VLAN 2 for the phones, I believe we would mark all the ports with phones as Untagged. The uplink ports would be Tagged as VLAN 1 and VLAN2 so they can see both regular network traffic on 1 and phone traffic on 2.
3. Would I have to configure switch ports to systems (Mitel) that dish out the phone details and other computers that do call recording as both VLAN 1 & 2 also? Should they be on the POE switches with the phones even though they don’t require power?
4. Currently the phones get their IPs via DHCP, would they still be able to see the DHCP servers since the phones would be on V2 or do the DHCP servers also need to be tagged as V1 & V2?

Thanks for your advice!