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looks like you aren't the only one with this issue.

https://www.reddit.com/r/apple/comments/567bgh/iphone_7_plus_anodization_wear_tear_2_weeks/

iphone rubbed wrong.png
 
Not experiencing anything of the sort. I take my phone out of a pouch probably 50-60 times a day which causes significant friction and I'm not seeing any wear.
 
I don't have the issue on my current phone, but I did have to get a replacement, and I noticed some slight discoloration in the same spot on the first one I had after only a couple days with the phone. Maybe there was a bad batch of anodizing? Who knows
 
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