5G technology hasn't been around as long as 4G, and thus not every radio site is equipped with 5G service yet - in contrast to 4G which is considered EE's base layer.
In this case your phone is connecting to a closer site than your router, which is correctly preferring a more distant site with 5G service.
If your router has any options for network-modes, you could potentially disable 5G or lock to 4G, and the router should then get similar performance to your phone, all else being equal.
