It sounds to me like you are doing a Wi-Fi speed test on your phone?
There are lots of things to consider.
First of all these third party devices test that specific devices speed to the websites server. This can vary depending on the device, location of the server and network traffic.
Wifi performance can vary significantly depending on the environment and has physical limitations compared to Ethernet connections.
If you have the black hub 4 your WiFi speed would be limited as this is only a WiFi 5 router. If you have Sky Q the speed would be limited even more as Q nodes can bottleneck throughput to around 100Mbps if near a Q node.
If you have the white hub 6 then you should expect better WiFi speed than the hub 4.
Other considerations are what other devices are running on your network at the time. Gaming PC's, consoles and cctv are examples of things that can hit the network hard.
Bottom line is for an accurate measurement of your speed you should use a wired connection. But also consider that the majority of devices can't use anywhere near gigabit speeds. As an example, streaming Netflix in 4k uses around 30Mbps. Having Gigafast means that more of these streams are possible simultaneously.
I would bet that your connection is spot on.
