Found the issue.
Apparently *86 is defined as block last caller by default in the obi star codes. It's possible this code got dialed to check voice mail.
This post offers a solution on clearing the block listing using just a star code
https://www.dslreports.com/forum/r30641411- .
What's interesting is the obi admin guide makes no mention of the block code but rather cancel repeat dial for *86 . Talk about a disconnect. This probably got changed in some firmware update but never documented.
All the more reason why change logs are important!A different obi, which was recently factory reset (following the 5757 firmware update) also shows block last caller for *86.
I changed *86 to *8686. Left the *99 in there too, just in case.