Remove username href

[Lynne]

Maybe try:
<phrase 1="" 2="$lastpostinfo[lastposter]">$vbphrase[by_x]</phrase>

However, this will give an empty link for the poster.

If you want to totally remove the link, then you need to edit the phrase also:
From: by <a href="{1}" rel="nofollow">{2}</a>
To: by {2}

(this has not been tested by me, so try at your own risk.)