We were having supper when the phone rang

We can often use the simple past to describe the action in progress, but the progressive puts more emphasis on the duration of the action, as in the second of these two examples:

While I fumbled for some money, my friend paid the fares.

While I was fumbling for some money, my friend paid the fares.

In the same way, still can emphasize duration:

Jim was talking to his girlfriend on the phone when I came in and was still talking to her when I went out an hour later.

6 Developing or changing situations in the past:

It was getting darker. The wind was rising.

The unemployment rate was increasing.

7 Repeated actions – criticism. ( This use is similar to that of the present progressive).

When he worked here, Roger was always making mistakes.

He was always ringing me up.

She was noisy and brash and constantly trying to attract attention by any means.

8 Just as the present continuous can be used to express a definite future arrangement, the past continuous can express this sort of future in the past:

He was busy packing, for he was leaving that night. (The decision to leave had been made some time previously.)

Why didn’t you tell me you were starting?

He didn’t know how he could inform them that he was not coming.

9 We use the past continuous tense in descriptions. Note the combination of description (past continuous) with narrative (simple past):

A wood fire was burning on the hearth, and a cat was sleeping in front of it. A girl was playing the piano and (was) singing softly to herself. Suddenly there was a knock on the door. The girl stopped playing. The cat woke up.