Hot soup is incredibly acidic? (3)

I believe the answer is:

pho

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

'soup is incredibly acidic?' is the definition.
I know nothing about this answer so I can't judge whether this works.

'hot' is the wordplay.
I cannot really understand how this works, but
'hot' could be 'h' and 'h' is found within the answer.
The remaining letters 'po' is a valid word which might be clued in a way I don't understand.
This may be the basis of clue (or it may be nonsense).

Can you help me to learn more?

I've seen this clue in The Telegraph.

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