I'm not a he, and I'm using a Garmin phone, but other than that, what you've said is exactly right!
I'm not up to landings yet - this was my first lesson that wasn't a TIF. What I was trying to work out was how much variability in height I had over the runway, and how high above the runway I was flying. At first I thought the altitude readings were wrong, and I should compensate using the altitude of ground level, but when I looked into it further, I saw this behaviour where although I knew I was on the ground, the GPS didn't.
I don't look at the phone at all in flight; at certain points I don't even look at the instruments, I'm concentrating on flying the plane straight and level 40 ft above the runway. but I'd like to know if I achieved this in the post mortem.