Since the thread has diverted substantially from the originally posted question, after typing the answer just discovered that it has been solved already.

According to PHD doc "large" is identical to "blocksize 32" , which could be in range 20-64 ( never tried blocksize).

PHD('INDEX,KEEP ALL,FULL,NUMBERS,LARGE')

I am able to search for "dimethyltrifluoromethanesulfonanilide" after that. Strictly speaking
only "dimethyltrifluoromethanesulfonan" ( first 32 characters ) was saved in index , but in this case ( exceeding 32 limit )
PHDbase returns as a hit any word having first 32 identical to what was saved. It is a different behaviour to the regular words
within 32 limit which require exact match or asterisk when indexed with "full".

P.S. Diverting from the topic again since Phdbase is not supported or developed any longer and author is unreachable for mere mortals
did anyone approach him asking about possibility to buy the source code ? It is quite typical now to include a source code and adjust pricing ( with or without ) for many third party tool vendors.