VLANs between Aruba and Netgear for VoIP

Here's the goal: Connect VoIP phones to their gateway by going through the existing Data network.

Here's the environment:

Most of the main building has network drops with 2 wall ports; 1 for the VoIP network (192.168.1.x/24) and 1 for the Data network (10.0.1.x/24). VoIP network is completely segregated. Clients (Polycom phones) plug into (a wall port -> patch panel ->) a Netgear Prosafe GS752TP (Switch 1) and then into an EdgeWater 4550/v2 gateway device (Gateway IP 192.168.1.1) and get their IP with DHCP.

However, we have one building (more of a trailer) that is connected only to the Data network. The switch out there is an Aruba HP 2530-24G Switch (J9776A) (Switch 2) which connects to the main building into another Prosafe GS752TP (Switch 3). Currently there is no routing or VLAN configuration, all ports on all switches are simple access ports, including the ports linking Switch 2 to Switch 3.

I need to put some phones in the other building. My plan was to (on Switch 2) create a VLAN for voice (we'll call it VLAN 25), tag specific ports on Switch 2 as VLAN 25 so anything plugged into them (phones) would be tagged as VLAN 25, tag the link between Switch 2&3 with VLAN 25 to ensure network traversal. Then on Switch 3 create VLAN 25, then tag the link to Switch 2 with VLAN 25. Then I'd need to connect physically Switch 3 to the EdgeWater gateway, and tag that link with VLAN 25 so that only VoIP traffic will get routed to that gateway, and everything else will continue to the regular 10.0.1.1 gateway.

I've been at this for a few hours with various tweaks to configuration, all with no success. Any guidance would be greatly appreciated!

Edit: I put Routing flair, but that might not be the most appropriate. It kind of falls under Design and Troubleshooting as well