First time flyer and I managed to flip my Phantom 3 Pro upside down. I was landing in grass, and I don't know if the ground had a rock or something that I didn't see, but the drone slowly rolled backwards and flipped completely upside down. I panicked and ran over and got ahold of the thing and got it upright. It was upside down with motors going for maybe 5-8 seconds. The motors emitted a rather loud higher pitched whirl sound during this.

Afterwards I was able to take it on a couple brief flights without issue. I don't think any significant damage took place as if flew just fine.

But did I just shave off a ton of life off the poor motors?

Thanks in advance.

Probably no damage at all.
In future, try shutting down by holding just the left stick straight down for 3 seconds after landing.
That way the Phantom won't want to tip over.

You could have landed on a slight incline causing the flip. If you were able to fly it around afterwards and if it doesn't sound any different than before then you should be ok.

Glad you came through it OK.
Make sure you push the left stick straight down and not to the left or right as that can make it tip.
Check your motors by spinning them by hand listening for grittiness.

Hmmm..... maybe an idea for a RC lawnmower.       Just kidding, I suspect it is fine.  I've taken to using a landing pad to assure a flat surface and keep it out of the grass and flying dust.

been there, done that! As Aeromirage suggests just hand turn props and listen but I'd say if it's up and staying up don't worry.

Time to buy a P4P