The most common and most likely answer to this crossword clue is the 14 letter word GHETTO-BLASTER
G
H
E
T
T
O
-
B
L
A
S
T
E
R
Buddy explains!
The straight part
We know that "portable (usually large)" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case portable (usually large) = ghetto-blaster.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.