The most common and most likely answer to this crossword clue is the 4 letter word VIGO
I've seen this crossword clue in The Times
V
I
G
O
More clues leading to the result VIGO
Buddy explains!
The straight part
We know that "Spanish port/r" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case spanish port/r = vigo.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.