Is it permissible for a girl to talk on the phone with a young man with the aim of getting to know their personalities to make a decision about marriage, with the parents' knowledge and approval, and provided that the conversation is within the bounds of Islamic law and does not include words of love or flirtation, and if the girl is confident that she will not be tempted by fitna, knowing that this method is common and acceptable in the questioner's country and involves no deception or harm? What is the difference between this type of acquaintance and acquaintance after engagement from the perspective of Islamic law?

The fundamental rule concerning a woman conversing with a non-mahram man is prohibition, unless there is a need and within the limits of Islamic guidelines, especially if she is young, as this is more likely to lead to temptation. Communication between an engaged couple (fiancé and fiancée) is not considered one of the recognized legitimate needs. Sheikh Ibn Uthaymeen mentioned that such conversations are rarely free from desire or pleasure.

As for looking at the fiancée, it is not permissible unless one has firmly decided to propose and has a strong presumption that the proposal will be accepted; otherwise, it is not permissible. What you mentioned about mutual acquaintance between the two parties through conversation and discussing economic, religious, and social matters is an undesirable overreach that opens the door to temptation, and Islamic law came to block all means (to evil).

A believer should not absolve himself by claiming to be safe from temptation; rather, he must seek safety and follow the path of caution. "Whoever guards himself against doubtful matters has indeed cleared himself (in regard to) his religion and his honor," and "Leave what makes you doubt for what does not make you doubt." The fiancée remains a non-mahram to her fiancé until the legitimate marriage contract is concluded.