Is it ethical that the PhD student is not offered a chance to become the communicating/ corresponding author?
Things might vary across fields, but I think that you might be overestimating the impact of being the corresponding author.

In my experience the corresponding author handles the communication with the journal (hands in the article and revisions, copyright form, etc). Furthermore, you might get a question every once in a while from a fellow researcher, but they are mostly like: "can you send me the article", or "may I use your figure".

Reasons for your PI to insist on being the corresponding author might be that articles may get questions long after you left the institution, and in some fields the corresponding author indicates who is the PI.

I would not worry too much about this. When your publication list is assessed, people will look how often you are the first author (when that is applicable for your field, some fields put the authors in alphabetical order). And when somebody has a question about the content of the article (which happens less frequently than you might expect) they either write you directly, or your PI might forward you the question.