Questions & Answers about Простите, я заработался и не мог вам позвонить.
How exactly does the combination of за- and -ся change the meaning of работать here?
This specific prefix and postfix combination creates a meaning of absorption or excess. It shows that the subject got so caught up in the action that they lost track of time or overdid it. By wrapping the base verb работать (to work) in за-...-ся, it becomes заработаться: to get completely carried away with work.
Is заработался a perfective or imperfective verb?
It is perfective. Verbs formed with the за-...-ся pattern to express getting absorbed in an activity are perfective because they focus on the result: the speaker has successfully entered that state of being 'carried away' and the consequence is that they forgot to call.
Why use the imperfective не мог instead of the perfective не смог?
The imperfective не мог describes a general, ongoing state of inability during that time. If the speaker had used the perfective не смог, it would imply a specific failed attempt (like 'I tried to call you, but my phone died'). Because he was lost in work, he didn't even make an attempt, so the state-focused не мог is the natural choice.
Just to be sure, why is it вам позвонить rather than вас позвонить?