Is necessarily to be in phase (3)

I believe the answer is:

has

I'm a little stuck... Click here to teach me more about this clue!

'is necessarily to' is the definition.
I can't tell whether this defines the answer.

'in phase' is the wordplay.
'in' says the answer is hidden in the clue.
'HAS' can be found hidden inside 'phase'.

'be' acts as a link.

Can you help me to learn more?

(Other definitions for has that I've seen before include "Enjoys" , "Eats" , "Cheats" , "Owns, holds" , "Bears" .)

I've seen this clue in the Evening Standard.

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