You're right; the first sentence IS about the future. The speaker could have said, "When will you speak with her again?" However, there is a subtle difference between the two sentences.
When the sentence is posed in the future tense, it an open question about WHEN will you speak with her again. It is asking about some time in the future. There is no assumption about when in the future this may occur and could be the next day, next month, next year, not yet known, or even never!
By contrast, in using the present tense to talk about the future, the speaker inserts certainty into his question. That is, he assumes that the other person will in fact speak with her again, the only question is exactly when. So while he asks, "When do you speak with her again?" he is assuming that this will definitely occur and relatively soon (tomorrow, in a few days?). He would not ask the question in the present tense if he didn't think that the fact that the two would speak was a certainty. He would also not use the present tense if he expected an answer in the distant future, for example, in six months or next year. Instead, he is asking a question to narrow down exactly when in the near future the two would talk again (e.g., tomorrow morning? before the weekend?).
Similarly, if the other person answered, "I speak with her on Thursday," then the use of the present tense regarding future actions/events would imply great certainly, that is, the fact that the two will speak is already arranged, agreed upon. Of course one could also convey more certainty by giving exact details: I will speak with her again tomorrow morning, I will definitely speak with her again before the weekend but we haven't arranged a time yet.
It is very common to use the present tense to talk about events/actions in the future that are certain and/or already arranged, for example, my flight is at 4 pm on Thursday. the conference call is on Friday.
To elaborate, the use of the present tense "When do you speak with her again?" implies that the other person has already scheduled a time to speak with her, whereas the future tense "When will you speak with her again" implies that the other person is intending to speak to her at some time, but has not yet set up a specific time to do so.
Though I would disagree that the present tense necessarily implies near future. If I take a trip to see a friend on the other side of the world, who I visit only every couple of years, but nonetheless make a credible promise that I will visit them again in, say, July of the year after next, someone else who knows that I have this sort of arrangement could still ask me 'When do I visit them again?'. Though that set-up is a bit artificial, I still think it is semantically valid - it's not the distance into the future, so much as the fixedness of the date, that determines which version is appropriate.May 2019