The only thing that I could find was from 2017, where phonearena were apparently re-injecting ads using WebRTC to bypass adblocking. So perhaps you are using an old blocklist such as this: https://s3.amazonaws.com/lists.disconnect.me/simple_ad.txt.
Thanks for the info. I found the raw blocklists on the router and the domain is in the 'disconnect' list, which I believe from a bit of reading is a tracker blocker list:
Z:\adblock-temp\extracted\adb_list.disconnect (1 hit)
Line 1367: com.phonearena
I did check the .json source files at the disconnect github page (about a month old) and the site is not listed. Beyond that I have better things to do with my Sunday!!