I'm planning to get two mesh routers (probably ASUS), but need a 3rd router to be able to have an IPT work phone in a certain location. Considering speed isn't a concern with the 3rd router, can I use a non-mesh router I already have for that 3rd location to wirelessly connect to one of the mesh-compatible routers?
So...
ISP <wired> AiMesh router <wired/wireless> AiMesh node
<wireless> non-AiMesh repeater/extender/media bridge <wired> IP phone
... yes, if the existing router supports repeater/extender/media bridge modes. Note that a media bridge uses all of its WiFi for its wireless bridge, so only supports wired clients.
Subject to how well it all works together... repeater/extender mode WiFi is not as smooth as AiMesh, in my experience.
If the IP phone router can be wired instead of wireless, then also consider using AP mode, if available on that router.
Ideally, skip the third router complication and wire the IP phone to an AiMesh node, or use a softphone app on a wireless mobile device.
Another option, keep the existing router as the non-AiMesh network router and wire AiMesh to it in AP mode with a wireless remote node for the IP phone:
ISP <wired> non-AiMesh router <wired> AiMesh AP <wireless> AiMesh node <wired> IP phone
OE