If the original phone is plugged into the hub instead of the wall socket , the volume of the original phone ‘ ringing’ shouldn’t be altered….if connecting it into the router instead of the wall socket has changed the location of the phone , and the new location is further away , or in a more enclosed place , so the phone is quieter because it’s further away from where your mother normally sits ( or whatever ) that got nothing to do with DV,
I’d suggest checking she hasn’t inadvertently altered the volume setting of the ringing on her own phone when moving it from the socket to the router
