Would a "partially phased" Barclay equal an "energy pattern"?
Whenever we hear of energy patterns in the transporting context, they seem to be separate from the phased matter stream that stores the physical person - say, Picard in the mentioned "Lonely Among Us". So using the terms as synonyms is probably nonstandard. But there's nothing to say it wouldn't be
allowed in the Star Trek universe.
A possible explanation for the 2 Kirks in "The Enemy Within" could come from the yellow powder being a natural filter that caused the transporter to only deposit half of Kirk's neural energy into his body upon rematerialization.
Now there's a cool idea!
That duplication body could have been from left over energy from the beam up as that episode identified velocity balancing as part of the process so transporters with the normal help of the engines are automatically adding/removing energy from the transporter pattern.
Every time we get transporter duplicates, or people who are enlarged or cut down in size by the transporter, we risk making it possible to use a transporter to create infinitely many copies of a person. Again, immortality, especially if the famed neural energies can be handled separately.
It would be much safer to try and postulate that only the original matter can ever be used to create anything at the other end of the process - probably because only the original matter contains all the information needed to put together the final product, and nobody else has any separate cache of information that would be needed to turn bulk matter (or matter created on the spot) into the final product. But then we need a different explanation for the duplicates...
OTOH, technobabble already exists for a variety of explanations. In the episodes dealing with the phase cloak, and in "Time's Arrow", it appeared that phasing meant nudging something ever-so-slightly backward or forward in time, so that it falls out of synch with the rest of the universe. Now, on the other hand the Star Trek universe is full of anomalies on the flow of time. There are many instances where there are two of a character, say, two Picards in "Time Squared", due to time travel. We only need to assume now that transporters and other "phase technology" applications are even more susceptible to time anomalies than normal matter is, because they already involve time travel of sorts. If anything goes wrong with the "phase nudging" or, in other words, "time nudging", then it's eminently possible to get two of something without inserting any new matter. It's just something inherent in time manipulation, everywhere in Trek!
(Perhaps there's a bill to pay at the Last Trump or something, tho. We don't know if such time travel really is a game of balances. But our heroes don't know it, either, and they have managed to travel in time just fine so far.)
Timo Saloniemi