You would need to unplug the router that is connected to the modem, and plug the TP link one in, using the existing red cable. If you follow the installation instructions, it will tell you how to login to the TP link, and start the setup wizard which will guide you through the options.
Make sure you know the BT login details for the BT router, as these will be needed when you run the setup wizard.
https://static.tp-link.com/2020/202008/20200812/7106508692_TL-WR841N&840N_QIG_V1.pdf
Its the router mode you need.
I am not familiar with this device, but it should be quite easy to configure.
OK that's a FTTP Optical Network Termination (ONT) so that's why you get faster internet.
I suspect you also have a slower service via the Phone socket to the right.
Back to the original issue.. Using the ONT connection, what router is connected to it? Can you provide a pic?
Its the left hand one you need to use. You just need to find a router that will work with your phone.
The one I suggested is the cheapest, but you can get others with a Gigabit WAN connection, which would give you the best speed, but they tend to be more expensive. The cheaper one will prove the issue.
@meg_ wrote:
That’s brilliant thank you! And my login should be in the format of firstname.surname@btconnect.com with my password is that right?
Whatever you have been told to use. You can always look at the BT router settings, as the information should be in there, just to make sure.
The initial login to the TP Link web interface, would be that specified in the setup guide.
@meg_ wrote:
What is plugged into that USB port?
@meg_ wrote:
A 4G booster incase my router goes down all of my devices will use the 4G stick
That would be BT Assure, and would not work with any other router. To be honest, you are unlikely to lose a fibre connection unless someone damages the external fibre route.
The TP link router is likely to be slower, as it has a slower WAN connection, but the object is to prove whether its the BT hub which is blocking your phone, so there is no point in spending a lot of money doing it. If it does not help, the you could probably return it.