iPhone 11 Pro with good wifi signal, but slow wifi speed

I have an iPhone 11 Pro that has the wifi bars showing full signal, but it runs slow on the internet. I ran a Comcast and Google speed test on this phone where it is getting 10-15 Mbps. I have an XR that I have sitting side by side with the 11 Pro showing full bars on wifi signal and when I run the same two tests, I get in the 300 Mbps range (we have Comcast Gig speed service) and I am not running them at the same time and nothing else is running on the wifi during these tests. I have tried with cell on and in airplane mode and different ways. I have done online searches, read on Apple community and such where there are a lot of ideas and we have tried all. I even went through my Comcast modern, Comcast Xfi setting and such, but see nothing. In the house we have an XR, 2 iPhone 11's and this 11 Pro. All but the 11 Pro run fast on the wifi.