Fill in the blank with the correct form of tense: While I _________ to him,…

Concept: When an action was already in progress at a specific point in the past and a second, shorter action interrupts it, English marks the ongoing action with the past continuous (was/were + verb-ing) and the interrupting action with the simple past. The auxiliary agrees with the subject: 'was' for I/he/she/it, 'were' for you/we/they.

Application:

1. The clause 'his phone rang' is simple past, marking the interrupting event.

2. The blank describes what 'I' was doing at that exact moment, so the ongoing action needs the past continuous.

3. The subject of the blank is 'I', so the auxiliary must be 'was', giving 'was talking'.

Cross-check -- why the other forms do not fit:

• 'Is talking' is present continuous, but the interrupting clause 'his phone rang' anchors the whole sentence in the past, so a present-tense form is out of place.

• 'Had talked' is past perfect, which marks an action already finished before another past event. The talking was still going on when the phone rang, not completed beforehand, so past perfect misrepresents the timing.

• 'Were talking' is the correct tense (past continuous) but the wrong auxiliary -- 'were' pairs with you/we/they, while the subject here is 'I', which takes 'was'.

Result: was talking