The most common and most likely answer to this crossword clue is the 3 plus 3 letter word CUT OFF
I've seen this crossword clue in The Daily Telegraph
C
U
T
O
F
F
Buddy explains!
The straight part
We know that "Put phone down" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case put phone down = cut off.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 CUT OFF mean?
CUT OFF adjective- Having had shirt sleeves or pantlegs shortened by cutting material from the end.
- The point at which something terminates or to which it is limited.
- A road, path or channel that provides a shorter or quicker path; a shortcut.
- A device that stops the flow of a current.
- A device for saving steam by regulating its admission to the cylinder (see quotation at cut-off).
- A cessation in a flow or activity.
- The player who acts directly before the player on the button pre-flop.
- (chiefly in the plural) shorts made by cutting off the legs from trousers
- A horizontal line separating sections of the page.