C7800 Poor Wifi

We bought the C7800 in january as we had to change ISPs with our move. We have spectrum, and  pay for a gigabit. I understand we wouldn't actually get a gig. Through wifi, if i am standing next to the router, my phone  (Galaxy S10 plus) gets 80mbps. My PC, which is wired, struggles to get 600 (Which is fine obviously) Yet my phone rarely gets 10 mbps if i leave the office.   Its been sugested that I get a stronger ethernet cord for wired connections, which I am fine with, but I should be getting more than 6mbps in  my tiny house (1200sqft).  Changing the channel makes virtually no difference in wifi speeds.

Next to router:

2.4Ghz (84Mbps)

5Ghz (265Mbps)

15 feet away in living room:

2.4Ghz (23Mbps)

5Ghz (112Mbps)

I test my speeds via the google speed tester.