The most common and most likely answer to this crossword clue is the 8 letter word MOBILISE
I've seen this crossword clue in Independent
M
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More clues leading to the result MOBILISE
- Phone about island rally
- One's phone rings in rally
- One's invested in phone for rally
- 18 might be impossible if short of shillings and pence
- Is caught hacking into a phone — take action!
- To rally crowd, I tell a story about head of state
- Is found hacking into phone — take action!
- Call men up for impossible manoeuvres without a second thought
- One’s phone rings, getting ready for action
Buddy explains!

The straight part
We know that "To rally" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case to rally = mobilise.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 MOBILISE mean?
MOBILISE verb- To make something mobile.
- To assemble troops and their equipment in a coordinated fashion so as to be ready for war.
- To become made ready for war.