I'm trying to find a way to remember which aspect to use with negated verbs:-

Я не позвонила - I failed to phone.
Я не звонила - I didn’t phone.

I'm finding it hard to just remember the 'rule' that 'failing to phone when you said you would' should be expressed as perfective, so instead I'm trying to see this situation from the point of view of whether something was successfully completed or not (which is an idea I find easier to bear in mind):-

1st one: I didn't phone during the time that I was supposed to. That time has gone, therefore the action I performed was 'not phoning', which I completed successfully.
2nd one: I didn't phone, regardless of whether I was expected to or not, therefore I simply didn't engage in any instances of phoning.

Is my 'logic' about this at all accurate? Or am I approaching this matter in a way that isn't going to be helpful?

How would you explain these 2 example sentences in terms of choice of aspect?

Thanks.