When I switch my PS on and connect to wifi speed drops

When I switch my PS4 on and connect to my wifi (Bt) the whole house wifi speeds drop dramatically. I do a couple of different speed tests on my phone and get constantly between 28 and 30mps download and 10 upload. The second the ps connects the speeds drop on my phone tests down to 2-5mps download and 1 upload. The second I disconnect or switch off the PS the speeds go back up to over 20. This happens for both my PS4 and my sons PS5. Can anyone help. Cheers.