My phone connects to a 5 GHz network when I need a 2.4 GHz connection for internet of things.

[lifeonmars · Accepted solution]

Depending upon which BT Smart Hub you have

On BT Smart Hub you can separate the Band widths (SSID)  in Router settings and give them each a name 

and connect your device to the SSID you wish

whilst on the BT Smart Hub 2 you can  only switch off the 5GHz or 2.4GHz  in router settings  

https://www.bt.com/help/broadband/fix-a-problem/broadband-and-wi-fi/i-want-to-improve-my-wi-fi/how-d...

[Bilco]

Thank you lifeonmars. Seems like a backward step by BT, but I understand I can go back to the previous settings when all is connected.