Select the appropriate verb forms to fill in the blanks in the given…

The correct answer is Option (2) → had phoned, wouldn't have had

Third conditional:

• It imagines a different past: an action that did not happen and the result that would have followed it.
• Pattern: If + had + past participle, would (not) have + past participle
  • If-clause: “had phoned”
  • Main clause: “wouldn't have had” (had to pay → would not have had to pay)
• Complete sentence: If I had phoned to renew the books, I wouldn't have had to pay a fine.
• This sentence: the speaker did not phone, and the fine has already been paid, so the condition is about the past and can no longer change.

Why the Other Options are Incorrect?

Option 1: phoned , wouldn't have — Incorrect. "If I phoned ... I wouldn't have to pay" is the second conditional, which imagines a present or future situation, not the past.
Example: If I phoned the library today, I wouldn't have to pay a fine.

Option 3: have phoned , wouldn't — Incorrect.

• “If I have phoned” puts the present perfect into the if-clause of an imagined past.
• “I wouldn't to pay” has no main verb, so the pair does not make a conditional.

Option 4: phone, didn't have — Incorrect. A present tense in the if-clause ("if I phone") cannot be joined with a simple past result ("I didn't have"). The tenses do not match.

Contrast: had phoned ... wouldn't have had (third conditional) imagines the past. Phoned ... wouldn't have (second conditional) imagines the present or future.