I pasted your regex into my script exactly and it didn't work either :(. I found one that did, though.
     First, I want to make sure I understand yours. Please tell me if the following is correct...
/^PH(?:.{0,4}|.*(?![HI]-000).{5})$/

1. starts with PH
2. (?:)these parentheses aren't memory parentheses
3. followed by 0 to 4 of any character or zero or more of any character
4. (?!)return true if "H-000" or "I-000" would not match next
5. followed by 5 of any character
6. followed by the end of the line

     At first, I thought it failed because of the .{5} part. So, I changed it to {4,5} because the possibilities are "?H-000" (only 4 characters after the H) or "I?-000". That still didn't work. I was confused about why you used the (?:) and the quantifier and the or after the first wildcard dot, so I removed them. It still didn't work.

     After all that I re-started. I counted the characters between the PH and the part I wanted to check (\d{19}) and tried /^PH\d{19}[^I][^H]-000$/. It's a little easier because all of these files have a fixed format. That did work, but I wasn't sure I needed to quantify the characters between the PH and the end of the file name. So, I ended up with /^PH.*[^I][^H]-000$/ which works fine.

     I'm not sure why I couldn't get yours to work. I haven't used regex extensions or assertions before, so I want to understand them better.

Many thanks for your input.

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        GhodMode