Sounds like you're using this script to cheat a trivia style game, but I'll bite:

You don't need to filter to an alias that uses regex, you just need to filter with the match as your %c.t1 thing

Code:
ON *:TEXT:*:#:{ 
  if (User == $nick) && ($5 == phrase:) { 
    filter -fk file.txt matchtest $6-
  }
}
alias matchtest { msg # Matched: $1- }

- argv[0] on EFnet #mIRC
- "Life is a pointer to an integer without a cast"