My devices get different WiFi speed when connected to the same 5GHz network on my Netgear R6100

I have an R6100|AC1200 router broadcasting at 5GHz (I've disabled the 2.4 GHz to reduce radio clutter).

Running the same internet speed test on my phone and laptop gives a download/upload speed of ~20 Mbps on my laptop but ~80 Mbps on my phone. When I connect my laptop to the router via ethernet, I get ~90 Mbps.

The strange thing is, when I first setup the router, I was able to get 80 Mbps (on the 5GHz wifi) on my laptop consistently. Additionally, when at work, I am able to get 200 Mbps on my laptop with work WiFi, so I don't think my laptop router has been significantly damaged.

This is the second time this issue has occured. The first time it did, I reset the router to factory and that seemed to solve the issue, but now it has recurred.

Any advice? Thanks people!