The most common and most likely answer to this crossword clue is the 6 letter word REDIAL
R
E
D
I
A
L
More clues leading to the result REDIAL
Buddy explains!

The straight part
We know that "Call again" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case call again = redial.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.
What does REDIAL mean?
REDIAL verb- To dial again
- Of or concerning a redia